Hello orochimaru700 Originally Posted by

**orochimaru700** Help proving these identities

1.) tanX-tanY / 1+tanX = cotY-cotX / cotXcotY+1

2.) sin5X + Sin3X / sin5X-sin3X = tan4X / tanX

Can I suggest first that: - you should copy the question down carefully; and:
- either learn how to write these things using LaTeX (lots of information available on this web-site); or:
- use brackets correctly.

I'm sure you mean for number (1):(tanX-tanY) / (1+tanXtanY) = (cotY-cotX) / (cotXcotY+1)

Anyway, enough of my ranting. Divide top-and-bottom of the fraction on the LHS by :

For (2) use the sum-to-product formulae. For example, the numerator becomes . Use a similar formula on the denominator, simplify and you're there.

Can you complete this now?

Grandad