## How to Measure a Central Angle

Three Little Kittens

Found their Mittens

So they shall have some pie.

Said one, “The size for me

is an arc from A to B

andjust shy of 360!”

Not quite sure what this little kitten was going on about?

Well, the central angle is one way we can use to measure circles.

As the name suggests, it is an angle with the vertex at circle’s center. Like this:

Here, we can see that the vertex is the center of the circle, with points A and B on the outer edge. Each side of angle ∠AOB is a radius, which means that it is half of the diameter.

The outer edge of the circle between points A and B—the kitten’s pie crust—is an arc. The arc length is the measurement between A and B along the curve.

Okay, now that we know the terms cold, let’s set up some relationships.

We can make up some ratios. The arc length from AB is a portion of the entire circumference. There is a direct ratio between the circumference of a circle and its measurement of degrees. The A circle has 360°. The central arc is a portion of that.

Let’s say we know the arc length was 25π and the circumference was 166π. We can calculate the central angle easily!

What if we only knew the length of one side of an angle and the arc length?

This is a bit more challenging, but it’s just an extra step.

Let’s recap with our original angle & circle:

Say OA was 6 feet. Arc length is 1.4π

We can calculate the circumference of the circle: Circumference = Diameter x π

The radius is half the diameter, and we know that AO is a radius because it extends from the center of the circle at point O and reaches the outer edge at point A.

Circumference = Diameter x π = 2(radius) x π
Circumference = 2(6 feet) x π
Circumference = 12π

Great job! Now, we can plug in the numbers into our original formula!

Yep, pretty small angle, all right. Let’s hope that’s not the one our kitty ended up with! Stay tuned to keep learning on online tutoring platform StudyGate.

Okay, here’s a brain zinger: if someone tells you that they are using the awesome Angle Addition Postulate, what do you think they are adding?

If you said “angles,” you would be 100 percent correct!

The Angle Addition Postulate basically means we are taking two angles and joining them together to make one LARGER angle!

Here’s a basic example”

We’ll take ∠GEM and ∠MEO

• Let’s join them together do that the angle converges at point E.
• We’ll also lay them together so that the two angles share the same border EM.

What can we do with the Angle Addition Postulate?

Great question!

Let’s look at the above angle again. If ∠GEO was 125°, then what is ∠GEM?

It’s almost like slicing a piece of cake!

∠GEM + ∠MEO = ∠GEO

∠GEM + ∠MEO = 125°

We know that ∠MEO = 90° because it is a right angle with the little square.

∠GEM+ ∠90° = 125°

∠GEM = 35°

Let’s go for something harder:

What are the angles below?

Easy!

First of all, we know that ∠ABD and ∠DBC follow the Angle Addition Postulate. This is because they share the same vertex at point B. The two angles share the same line BD, so they line up.

∠ABD + ∠DBC = ∠ABC

We know that AC is a straight line, and straight angles are 180°

We also have the formulas for ∠ABD and ∠DBC

Let’s plug ‘em in:

∠ABD + ∠DBC = ∠ABC

(5x+10) + (2x-5) = 180°

5x + 10 + 2x – 5 = 180

7x + 5 = 180

7x = 175

x = 25

So, now that we know what  is, we can plug it into the original formulas! ∠ABD = 5x + 10, x = 25

∠ABD=135°

∠DBC = 2x – 5, x = 25

∠ABD=45°

Let’s check:

∠ABD + ∠DBC = ∠ABC

We are balanced!

## Lord of the 45-45-90 Triangle

Triangles come in all sizes. Some are acute, some are obtuse, and some are just right.

The ones that are just right weren’t designed by Goldilocks. But she knew a right triangle when she saw it. She knew that a triangle was “right” when it had a 90° angle—perfect for drawing sharp corners. Like these:

But there was an even more special right triangles. She could hardly wait to contain herself when she saw it. It was the awesome 45 45 90 triangle. Here it is in its mighty glory:

• The two sides making up the 90° angle have the same length
• The triangle is half of a square, as you can see on the right.
• That means its hypotenuse (the diagonal of the square) is the side x √2

Pretty easy, huh?!

• The tangent of 45-45-90 triangles is always 1.

Can’t get any easier than that!

Let’s recap!

The angles are easy to remember: 45+45+90 = 180°

The sides and hypotenuse are easy: the two sides are the same! x = x

The Hypotenuse is x√2

Goldilocks is a Lord of the 45-45-90 Triangles.

And now, you are, too!!!

## Angling for Angle Pairs

There’s something to be said about angles:

“To think I will never see

An angle as complementary as thee.

An angle whose hungry mouth is open

To a supplementary pair unbroken

With a line, perpendicular or straight,

We a newborn angle doth create!”

While poets may sing the praise of angles, let’s set it down in basic terms.

• What’s an angle?

An angle is the measurement of degrees between two lines.

These are all angles. They are acute angles because the gaps between the two lines are less than 90o. Acute means small, and small things are cute. Aren’t they cute?

These are angles, too. They are obtuse angles because the gaps between the two lines are GREATER than 90o. Obtuse means “slow” and “unintelligent.” While we don’t want to be mean to our angles, we can think of them as a bit unwieldly and hard to manage. Why are these angles so obtuse, darn it?!?

This means that angles that are EXACTLY 90o are called right angles. As Goldilocks would tell us, not too large, not too small, just right. We can make little squares inside them to show that the corner is 90o sharp. Pretty cool, huh?

OKAY, now that we have that downpat, what do we do with our happy angle family?

• We can use angles to measure degrees.

For designers like architects, builders, and engineers, this is essential stuff…and for obvious reasons. If you’re measuring space and distance, whether for landscaping or for algorithms, angles are a must.

Let’s throw some basic calculations on how to measure angles.

These are pretty simple. It’s literally two angles next to each other! They share a common vertex (the point where they intercept) and one side. Here’s one:

For example, we see that the blue angle,∠BAD, has a measurement of 58o. The smaller angle ∠BAC has a measurement of 32o.  What is the measurement of ∠CAD?

Simple subtract!

58o – 32o = 26o

Easy, right?

• Complementary Angles

A complementary angle is a specific type of adjacent angle. These angles add up to 90o to form a RIGHT ANGLE.  Here’s one:

Since we know that the sum of the angles is always 90o, we can easily find out what one angle measurement is if we know the other. Since both angles are smaller than 90o, we know that all angles in complementary angles are acute.

• Supplementary Angles

Supplementary Angles take things a bit further. When we put two COMPLEMENTARY ANGLES together, they form a straight line, like this:

See how CO bisects DA? The angles on the right of ∠COA add up to 90o, right? That means that ∠DOC is also 90o. Put them together and we have supplementary angles.  Angles that are supplementary share the same vertex and one line. They form a straight line and add up to 180o. Dead on arrival, no?

Here’s another example of a supplementary angle, this time, without complementary angles.

Note that if one angle is less than 90o, the other must be greater than 90o to add up to 180o. Thus, unless the angles are right angles, supplementary angles include one ACUTE and one OBTUSE angle.

We can also complicate this by stating that in a circle, all the angles add up to 360. This is because two right angles sharing a vertex forms a straight line, but travels half a circle. If we join two more right angles at the same vertex, the degrees of measurement would go all the way around! Like this:

Got it? Right on target!

Now let’s mess it up a bit with multiple sets of angles sharing one line, kinda like a road map. Line Y is the transversal line because it joins Lines A and B by crossing them:

We can see that [D] and [E] are supplementary since they share the same vertex, one line (Line Y) and add up to 180o. What else can we say?

• Corresponding Angles

[E] and [Q] are corresponding angles because they share the same exact position on their parallel lines A and B. Their angles are the same. The same with [F] and [R], [D] and [P], and [G] and [S]. Let’s highlight them:

See how the angle pairs correspond. What else can we say?

• Alternate Interior Angles

We also have Alternate Interior Angles. Being interior angles, they are on the “inside,” between the parallel lines. These angles share the central transversal line, but have two different vertices. Think of them forming a letter Z and a reverse Z. In the example above, [G] and [Q] are alternate angles. So are [F] and [P]. Since Lines A and B are parallel,we can see that alternate angles have the same degrees.

• Vertically Opposite Angles

From Z to X!They are angles that share the same vertex and transversal, but no corresponding side. They also have the same degrees. Think of them as the Letter X, with the angles opposite each other. In the above example, [E] and [G] are Vertically Opposite Angles. They each have 80o. So are [D] and [F]. Each one has 100o. Check ‘em out below:

Now that you’re seeing crosses, we’ll have a quick quiz. Find all the angles below:

We only have a single degree measurement, 111o, but this is no problem!

Solve the SUPPLEMENTARY ANGLE first!

A pair of supplementary angles add up to 180o, right? We also know that 111o is OBTUSE, so its adjacent angle, ∠C, must be ACUTE!

∠C + 111o = 180o

∠C = 69o

From there, we can fill out the top set of angles pretty easy.

∠A is a Vertically Opposite Angle from 111o. We know vertically opposite angles have the same degree measurement. So ∠A is 111o

The same with ∠C and ∠B.

∠C is 69o so ∠B is also 69o.

To check, we can also ADD ∠A + ∠B to see if they add up to 180o. (They do!)

We can simply copy and paste the top set of angles of the bottom, but we also use our vast knowledge of angle pairings to figure ‘em out. You’re an expert—go right ahead!

∠G is a corresponding angle with 111o.

That means ∠G =111o

∠D is an alternate interior angle with 111o. They form the inverse Z shape!

That means ∠D =111o

We can either figure out what ∠E and ∠F are since we know their supplementary angles, which add up to 180o

Or, we can look at them in pairs.

∠E is a corresponding angle with∠B. Since ∠B = 69o, ∠E is also 69o.

∠F is a Vertically Opposite Angle from∠E. Since we just figured out what ∠E is, and we know vertically opposite angles have the same value, ∠F is also 69o.

SO:

∠A = 111o.

∠B = 69o.

∠C = 69o.

∠D = 111o.

∠E = 69o.

∠F = 69o.

∠G = 111o.

Congrats! You are now the Awesome Angle Master! Have a glimpse of Reference Angle.

## Trapezoid Training

If your first thought of a trapezoid was either a flying circus act or a muscle in the shoulder, this blog is for you!

First, a minor let down. A trapezoid is nothing exotic as double summersault through the air. But it is pretty nifty. This is a trapezoid:

What’s a trapezoid, then? It’s a shape with four sides. Of the four sides, two of them are parallel.

In this case, the top and bottom lines are parallel. The side lines will eventually intersect if they continue downward.

A trapezoid’s side lengths don’t matter. Two sides can be the same, as shown above. Or they can all be different, like these:

The top and bottom lines are still parallel, even though no two lines have the same length.

***Burning Question: Is a rectangle a trapezoid? Nope. A trapezoid can only have ONE set of parallel lines. Rectangles (and squares) have two sets! (Now ask yourself if a square can be a rhombus. To find out: see my next blog! 😊)

***Fun note: There is also a shape called a TRAPEZIUM, which is a four-sided shape with no parallel sides, like this:

This is not a trapezoid.

Now that we have a trapezoid, what do we do with it? How can find its area?

Why do we need to find its area? It’s like the old saying goes:

There was an old woman who lived in a shoe

She had so many sons, she didn’t know what to do.

So she sliced up the shoe, like a loaf, and gave them to her boys

“This is your home, enjoy the trapezoid!”

So, how much living space did each kid have?

Let’s say this is the cross section of the shoe slice:

How to figure out the area?

An area for a trapezoid is the SUM of the two parallel sides, divided by 2, and then MULTIPLIED by the height. The height is a perpendicular line between the two parallel sides.

Here we go:

So let’s give some dimensions to the shoe:

Let’s plug in those values:

Don’t forget this is squared meters since we are considering two dimensions! We multiplied the labels to get meters2

But the shoe slice also has three dimensions: length!

It is very easy to figure out the volume of a trapezoid! Simply multiply the area by its length!

Since we already know the area, let’s just say that the generous old woman gave each son a slice of shoe that was two meters long. Plug in the numbers again:

*Note that when measuring by volume, we are dealing with three dimensions, so the figure is cubed!

Hip hooray!

## Coterminal Angles Quickly Solved

All right, math wizards, here’s a trick question: does a circle have more than 360° in it?
The answer: nope. Once you go all the way around a circle, you end up back at the beginning! Pretty easy, right?
But that doesn’t mean an angle can’t have more than 360°. Here’s an example:

Say we’re on a Ferris Wheel. If the ride’s any good at all, you just don’t make one trip around and then get off. You keep on going for several rounds, right? For each revolution, we make repeated trips and the degrees we travel doesn’t just start over at 0.
We end up with a graph that looks like this:

So what does that have to do with coterminal angles? It’s pretty easy once we think about it. Say we traveled 45° on the initial go around.

Where we started is the Initial side of the angle. Where we stopped is the terminal side of the angle. Neat, huh?
If we were going in the opposite direction of the initial side, we would be going in a negative direction. In this case, starting at the initial side and going “backwards” to the terminal side gives us -315°. When we make a complete loop, degrees traveled will be 360° and the negative angle will be 0°. Makes sense, right?
But what if we kept going after we completed the loop and landed back at the terminal side? It would look like this:

See how we traveled from in a complete loop from the terminal side?
To find out how many degrees we traveled in, simply add 360° to the initial angle!
45°+360°=405°
We can say that 45° and 405° are coterminal.
But we can also do more! Coterminals can be negative as well. Remember the -315° from going backwards? That angle also shares the same initial and terminal sides.
Thus, 45°,-315°,and 405° are all coterminals!
*****BASIC RULE: just add or subtract 360° to your initial angle and you can find a coterminal. The possibilities are endless! Take a gander below:

63° and 2223° are coterminals. And we can keep going!
How else can we measure coterminals? Well, we don’t have to use degrees. We can use radians.
A radian is the measurement of an angle in a circle where the radius is the same as the angle’s arc.

How many radians are in a circle? Well, the formula we use is: there are 2π radians in a complete circle. We divide it like so:

Have a circle is π, and a complete circle would bring us back to 2π.
How much is 2π?
We know that π=3.14159….and then goes on forever and ever and ever.
That makes 2π=6.28318
Since there are 2π in a complete circle, that means there are 6.28318 radians in a circle.
The same principle applies to radians as they do degrees.
If we need to find a coterminalangle, we can add or subtract 2π!
It’s as easy as that.
Quick example: we have an angle with radian π/3. What is the coterminal angle?

If we want to find more coterminal angles, we can add or subtract 2π! The possibilities are endless!
Did you want to convert this measurement to degrees?
7π/3 × (360°)/2π→7/1×120/2→7×60=420°
Here are the basic formulas:
For coterminals of degrees -> add or subtract 360°
Here’s a quick cheat sheet conversion chart from radians to angles:

Congrats! You are now a radical coterminal angle wizard with the help of online learning StudyGate.com platform !

## How to Determine a Reference Angle

Here’s a secret that math tutors keep to themselves: Sometimes, the fanciest math skills are actually the simplest ones! Like the ultra-mysterious Reference Angle! Sounds pretty impressive, no?

But Reference Angles are actually one of the easiest things to define. Let’s draw a graph and an acute angle (an angle less than 90) and an obtuse angle (an angle that is greater than 90):

The Reference Angles are the measurement of degrees from the shortest distance between the terminal line to the X-axis.

For an acute angle, it is very simple. It is just the degrees.Inn  this case, it is 45°.

Fort an obtuse angle, it is a little trickier. The terminal line is actually closest to the x-axis on the OPPOSITE side of the angle. In this case, it would be this:

We know the degree measurement is 70° because the angles that make up a straight line through the y-axis is 180°. We just subtract 110° from 180° to get the REFERENCE ANGLE!

Easy, huh?

***Please note that even though the Reference Angle is on the negative side of the x-axis, it is always positive.

***Also, unless the terminal side of the angle is on the y-axis to form a right angle, the Reference Angle will always be acute!!!

In other words, Reference Angle 90°

Here is the largest Reference Angle possible:

It is right angle with a measurement of 90°

***We can use Reference Angles to calculate the functions of angles, like sine, cosine, and tangents. It’s basically a cool shortcut: the sin(70) and sin(110) are the same because they have the same Reference Angle!

Want to see Reference Angles in action??? Check out the link below:

http://www.mathopenref.com/reference-angle.html

## How to Prove There are 2 Similar Triangles

In the whole, wide world of geometry, there are so many shapes and sizes of triangles that you might think they’re all exactly the same, or that they’re all completely different. Not necessarily! Two triangles must share precisely specific traits in order to be deemed similar. If you’re faced with the puzzle of determining if there are two similar triangles, there are three different paths you can take to solve the mystery.

## Path 1: Use the Angle-Angle (AA) Method

If you can determine the angle measurement of at least two angles from each triangle, the AA method is your best chance of solving the similarity mystery. If two angles of one triangle are the exact same measurement of the same two angles of the other, the two triangles must be similar. It’s really just that simple!

## Path 2: Use the Side-Side-Side (SSS) Method

The SSS method is most helpful when you are given, or can determine, the length of all three sides of both triangles. If all sides on one triangle are specifically proportional to the corresponding sides of the other, then those two triangles must be similar. For example, if one triangle has a hypotenuse of 3 inches, and the second has a hypotenuse of 6 inches, those two sides are proportional because 6 is exactly twice the length of 3. If the other corresponding sides of the triangle are proportional, the triangles are similar and the mystery is solved.

## Path 3: Use the Side-Angle-Side (SAS) Method

When you’re faced with two triangles that have at least one given angle measurement, and two given side measurements, the SAS method is your best bet. If the corresponding angles of the triangles have the exact same measurements, and the corresponding sides are proportional to one another, then those two triangles must be similar. Just remember that the measured angle from one triangle must be in exactly the same place as the measured angle from the other, and the same principle applies to the measurements of the two sides as well.

## Graphing Functions: A How to Guide for Graph Calculator

Math brings out the artist in you!

While the industrious student can simply whip out a graph calculator to draw up graphing functions, figuring out functions the old-fashioned way can be pretty keen. With nothing but a pencil and a piece of paper divided into little squares, we can create lines and make ‘em dance to the curve of a slope intercept form.

We all knew math was a cute little number, but here is where we prove it!

Let’s take a simple equation:

y = mx + b

This is a pretty basic format for graphing. We have a Y axis that has a direct relationship with the X axis. The ratio between Y and X is determined by M.

Let’s throw in some numbers and see where they land:

y = 2x + 6

This is as easy as it gets. Let’s whip up a graph:

Let’s start easy, with x = 0.

So we know that when X is at 0, Y is 6. The “2” is the ratio between X and Y. If X was 1, then simply multiply X x 2 + 6 = 8.

We can create a quick chart between X and Y. Don’t forget that we can go into negative values for X and Y s as well!

 X Y -4 -2 -3 0 -2 2 -1 4 0 6 1 8 2 10 3 12 4 14 5 16 6 18 7 20

Then, plot the points and connect to form a line!

Pretty neat, huh?

****QUICK TIP: go back to the equation

We can break M down to represent the change over Y over the change over X. If it were a fraction, it would look like this: change over Y ÷ change over X

Since 2 is basically 2÷1, we can simply say that for every change in X, we move Y up 2 spaces! Look at the chart and do the math. See how it works?

What is M was a fraction?It still works out:

This means that for every X value we have, Y goes up by . The chart would look like:

 X Y -4 -1 -3 -.25 -2 .5 -1 1.25 0 2 1 2.75 2 3.5 3 4.25 4 5 5 5.75 6 6.5 7 7.25

Graphs with fraction M look less steep than graphs where M is a whole number.

But where does this get us with graphing functions?

It’s really easy: it’s basically the same thing!

ƒ(x) = x2 + 2

In this case, Y = F(x). Since the equation is squared, there will be some curves as the Y intercept changes from positive to negative. But the procedure is the same.

So let’s throw some X values in and see what we get!

 X Y -5 23 -4 18 -3 11 -2 6 -1 3 0 2 1 3 2 6 3 11 4 18 5 23

As you can see, we have a curve!

Imagine the possibilities: with numbers, you can draw anything!

## Basic Geometry: How to Find the Perimeter of a Rectangle

Finding the perimeter of a rectangle is one of the easiest first steps towards becoming a geometry genius. The formula is simple and quick, and with a little practice, you’ll be finding the perimeter of every rectangle in sight!

So what is the perimeter of a shape, exactly? Picture a large, grassy field with a fence around the outside. The fence represents the perimeter – it’s just the outermost boundaries of the shape. When we calculate the perimeter, we’re looking for how long the distance around the shape is.

The formula used to calculate the perimeter of a rectangle is 2(l + w). L stands for length, which is found by measuring the longer side of the rectangle. W stands for width, which is found by measuring the shorter side of the rectangle. Let’s say the length of a rectangular field is 10 feet, and the width is 5 feet. To find the perimeter of the rectangle, we would add 5 and 10, which equals 15. To finish the equation, we would multiply 15 by 2 for a grand total of 30 feet. It’s really that simple!

Now that you know how to calculate the perimeter of a rectangle, practice on any rectangle you can find. Your computer screen, your kitchen table, and your windows are just a few that are right inside your house. You’ll be a perimeter master in no time!

Online learning hub and study helper StudyGate offers homework help in various subjects. Whether students need to get instant homework help or online tutoring services, StudyGate is the one-stop solution for you.

## Geometry Help: How to Find the Volume of a Cylinder

One of the simple joys of life is a push-pop candy. You remember ‘em:

Right, a lollipop without a stick.

And while it sounds like a push-up, a Push-Pop doesn’t have the same effect.

(And no, eating one does not have the same effect as doing an actual push-up).

Back when I was a kid, I always wondered how much good stuff was in a tube. Thanks to the wonders of a simple math formula to calculate the volume of a cylinder, we can solve this burning question!

CAVEAT: (Ideally, the candy went all the way to the bottom of the tube, but we kids knew this was never the case. ☹)

Here’s the formula for the volume of a cylinder:

Hmmmm, this may look familiar to some of you. Here’s why:

This is a cylinder. It’s basically a tube that has the same width at every point. When you look at the end points, they are perfect circles.We know the formula for finding the area inside of a circle, right? , where r is simply the radius, or a straight line from the edge of the circle to the center.

Once we find out the area of a circle, we just extend it into a third dimension, which is the height. Multiplying the area by the height gives us the volume!

Let’s go back to our push-up candy!

Let’s assume I haven’t eaten it already.

Mine looks to be about 1.75 cm across and 4.5 cm tall. Yeah, they’re not as big as they used to be.

Here’s the formula: V = Πr2h

Since we know the diameter is 1.75 centimeters per pop, we can simply cut the number in half to get the radius.

1.75 ÷ 2 = 0.875 centimeters

Now, plug in the numbers:

V = Πr2h
V = Π0.8752 x 4.5
V = Π0.765625 x 4.5
V = Π x 3.4453125
V = 3.14 x 3.4453125
V = 10.82 cm3

Don’t forget the little 3 after the label. We are calculating in three dimensions.

Hurrah for the volume master! Time for a treat!

## Math Help: How to Find the Volume of a Triangular Prism

A triangular prism has rectangular sides and an equilateral triangle as base, as you can see above. Volume is the maximum quantity a three dimensional closed-shape can hold. Therefore, the maximum quantity a triangular prism can contain is called volume of a triangular prism. As volume is calculated of three dimensional shapes only, the unit volume is always expressed in cubic units. In this case, we’ll use inches here.

Look at this. Imagine someone just gave this to you, and you wanted to find out exactly how much sweet, sweet chocolate was contained inside. You would therefore need to find the triangular prism volume! How would you do it? What formulas would you use?  How do you find the volume of a shape? Once again, we can count on Geometry to save us. We look at this and see a long triangular box just waiting to be opened. The mathematicians of the world see this as a prism.

## How To Find The Volume

Volume of any triangular prism can be calculated very easily! We already know this formula for the area of a triangle:

We can calculate the area of the triangle base. Let’s say that in this case, b = 4, and h = 3. Simply calculate ½ times 4, which is 2, and then multiply that by 3, and you get 6 as your answer.

Then, we go to our triangular prism volume formula, which is:

To find the volume of our tasty triangular prism, we take what we’ve just done and multiply that by the length of the prism. Let’s say that L = 9. We would do 6 X 9, which equals 54. And that’s it! The volume of the Toblerone bar is 54 cubic inches!

So the next time you’re wondering how much deliciousness you’re getting, do some quick geometry with our handy triangular prism formula and enjoy yourself! For any further math help, you can visit Studygate.com!