Question

How do you prove `sin(pi/2-theta) = cos theta`?

Answer 1

Use `sin(a-b)=sin a cos b - cos a sin b`. Here, `a = pi/2 and b = theta. sin (pi/2)=1 and cos (pi/2)=0`.

Explanation:

This way, you can prove all similar results, like, for example, `sin(pi-theta)=sin theta`.