Finding an unknown angle measure
About this video
Angle Z, a 60-degree angle and another 60-degree angle together make 150 degrees. The video subtracts the two 60-degree angles (120 degrees in all) from 150 to find that angle Z measures 30 degrees.
You'll be able to
- find an unknown angle when I know the whole angle and the other parts.
- subtract known angle measures from a total.
- subtract 60 twice by subtracting 120 at once.
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.
- unknown angle
- An angle whose measure you need to work out.
Transcript
- [Instructor] We are asked, what is the measure of angle Z? And we could see angle Z right over there. And if you take the measure of angle Z plus this 60-degree angle, plus this other 60-degree angle, we see all of those angles add up to 150 degrees. So one way to think about it is, if I start with that 150, lemme make sure you can see what I'm doing.
So if we start with that 150 right over here, so this is going to be equal to 150 degrees. And if we were to subtract out these two 60 degreeses, so minus 60 degrees, and then minus another 60 degrees, that should give us the measure of angle Z. So this is going to be equal to 150 degrees minus 60.
And if I subtract 60 twice, that's the same thing as minus subtracting 120 degrees. And so that is going to be equal to 150 minus 120. You could write it up here if you want to. Many of you might be able to do that in your head. You would get five minus two is three, and then the hundreds, a hundred minus a hundred is just zero.
So you would end up with 30 degrees. You could do that in your head saying, okay, the difference here, the hundreds are just going to subtract out to each other. 50 minus 20 is 30 degrees, and we're done. That's the measure of angle Z.
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