We have to simplify the expression:
[tex]\cos (\theta+\frac{\pi}{2})[/tex]
We could see it graphically:
We see that for any angle theta, the cosine of theta + pi/2 is equal to negative sin of theta.
Then we can write:
[tex]\cos (\theta+\frac{\pi}{2})=-\sin (\theta)[/tex]
The answer is -sin(theta).
