Hello. I was doing a (simple) physics problem and stumbled with a mathematical problem. I was doing a projectile motions problem and I have set up my equation like this: Δx = Vi (cosθ) (t) 270= 25cosθ t t = 270 / (250cosθ) And this is where I'm having problems. I know from my high school trig that doing division by a trig function is invalid since cosθ can be zero. However, I see no other way to express t (time) with other equations I know. So, my main question is, is what I did a valid move algebraically? Are there any exceptions to that rule about dividing by trigonometric functions? Note: I actually saw a yahooanswer post about this but I really want to know physicsforums's say about this. I know this might come as an easy question for some but it really came very confusing for me. Help would be very appreciated.