
Some trig problems =/
I have some work and im confused on these problems... I did all i can (looked in book and such) and need help.
Simplify the expression cos (X5pie /2)
For this one i know that you can go to (cosx)(cos5pie/2) + (sinx)(sin5pie/2) But i dont know what to do from there
second is If cotx= 4/3 and 180degrees< x < 270degrees, find the exact values of sin2x and cos2x
Here, i know if there was a triangle, there would be the 5,4,and3 to it, but i dont know how you go to the sin2x and cos2x
third is Find the solutions of sin2x = cosx that are in interval [0, 2pie)
If anyone could help, youd be my hero. I have 8 tests this week and im stressing out on these problems....


Ty again for your help. However just one thing that I found as these were graded. For the first problem it was +sinx .. not sinx :p