CPM Homework Help : CCA2 Problem 8-162

Use your knowledge of the unit circle to explain why the graphs of $y = \sinθ$ and $y = \cos(θ -\frac { \pi } { 2 })$ are the same.

Hint:

$\frac{\pi}{2}$ is equivalent to $90°$

Sketch a unit circle. Choose any angle. Find the sine and cosine of the angle. Now subtract $90°$ from your angle and find the sine and cosine again. What happened? If you draw an accurate reference triangle, it will help you see what is going on here.