First off, I'm not looking for answers, just trying to figure how I would solve certain problems. If I had a problem such as: sin A = -4/5 (-pie < A < -pie/2) Using this, find cos A, tan A, cot A, sec A, csc A. I know that I have to use identities, but how would I go about finding cos A? I can't find an identity that will allow me to find cos A using sin A -4/5. I guess I could use sin^2 -4/5 + cos^2 A = 1, but how would I solve that? Also, I have absolutely no idea where to start with this problem: -4cos((2x/3) - pie) + 2 = 0 Finally, which identity do I use for this problem: tan(4x/5) = -1 Help much appreciated.