00:01
Okay, so for this question, we are given the equation y is equal to arc cosine of negative a half, and we have to find the exact value.
00:20
So the first thing that we're going to do is we are going to rewrite this in terms of cosine rather than the inverse.
00:27
So we're going to do that by switching the places of y and negative a half, and we're going to get negative a half, is equal to cosine of y.
00:38
Doing so will help us find the angle a lot easier.
00:45
Now, since we're given half, the numbers 1 and 2, we can use the special right triangle of a 30, 60, 90, to help us find our reference angle.
00:56
So we're going to do that by drawing our triangle, 90, 30, and 60, label our place, place values, and then since cosine is adjacent over hypotenuse, we can see that the 1 and the 2 are for 60.
01:17
So our reference angle is 60.
01:24
However, since we're given a negative a half, we have to find where cosine is negative on the unit circle.
01:33
So using the unit circle, we know that all trig function...