Composing and decomposing angles
About this video
This video shows that a big angle can be made of smaller angles. Angle y is made of three 40-degree angles, so it measures 120 degrees. An 80-degree angle is split into four equal angles x, so each x is 80 / 4 = 20 degrees.
You'll be able to
- find the measure of an angle made up of smaller angles by adding.
- find the size of equal parts of an angle by dividing.
- check an angle answer by adding the parts back together.
Key words
- angle
- The amount of turn between two rays that meet at a point.
- degrees
- The unit used to measure the size of an angle.
- measure of an angle
- How many degrees an angle is.
Transcript
- [Instructor] So what I have here are two angles. Angle y, I wanna figure out the measure. I wanna figure out the measure of angle y here on the left. And then on the right here, I wanna figure out the measure, measure of angle x. So why don't you pause this video and have a go at it before we do it together.
So here, y is a big angle, it's gonna have a big angle measure, and y is made up of these three smaller angles. Each of them have a measure of 40 degrees. So this is going to be, and maybe I'll do it in that same purple, it's going to be 40 degrees plus 40 degrees plus 40 degrees.
So four plus four plus four is 12. So 40 plus 40 plus 40 is 120, 120 degrees. Now here, we have each of these x's. This measure of x plus it again, plus it again, plus it again, is going to be equal to 80 degrees. Or another way to think about it is we could start with 80 degrees and divide it by four.
So 80 divided by four is going to be 20, 20 degrees. And you can see that, 20 plus 20 plus 20 plus 20 is indeed 80 degrees.
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