1. The problem statement, all variables and given/known data I have an assignment that is to prove for instance the range of a projectile that is fired from 40 degrees will be the same as one fired from 50 degrees cause they are complementary but I need a general way to prove it for all angles less than 90 degrees. 2. Relevant equations sin θ = cos 90 - θ 3. The attempt at a solution I have searched the Internet and read my physics book and I under stand how to work out if they have the same range or not I'm just having trouble coming up with a general proof for it.