Thread: trig homework

I have two problems I need help with please.
1. find the exact value of tan(2u) using double angle forumlas given tan(u)= -2/9, pi/2<u<pi

2. use sum-to-product formulas to write the sum as a product?
sin(5theta) - sin(theta)

substitute (-2/9) for tan(u) and do the arithmetic.




substitute for a and for b.