Question

how sin(90+theta)=cos theta??

Answer 1

http://www.piglets.org/serendipity/uploads/sincos2.png

Answer 2

This is regards to the question you had about projectiles.
I think 45 degrees ends up being the optimal angle for maximum range.
So in the example here, whether you shot from an angle of 30 degrees or 75 degrees, you would land at the same spot.
Angle + 45 degrees.

Sorry I know this isn't in the right topic, I dunno where the other question went though.