00:01
In this question, we say on the graph of f of x equals the cosine of x and the interval from 2 pi to 4 pi, including 2 pi but excluding 4 pi.
00:11
For what values of x does the graph cross the x -axis? choose all of the answers that apply.
00:18
So we want to know where we cross the x -axis, where the y value on this function is equal to 0.
00:27
So in order to figure this out, we are solving the equation cosine of x equals 0.
00:34
To do that, i'm going to think about my unit circle.
00:40
So my unit circle, again, is my circle centered at the origin with radius 1.
00:46
Now, the cosine of an angle is the x -coordinate of the point on the unit circle.
00:54
And so the x -coordinate is equal to 0 at the top and the bottom of the unit circle.
01:02
Now, the top of the unit circle, that's usually that point there, 0 comma 1, associated with pi over 2 radians, while the point at the bottom of the unit circle, 0 comma negative 1, that's associated with 3 pi over 2 radians...