- #1

- 91

- 0

I have to prove that

(cos 3x - Cos 7x) / (Sin 3x + Sin 7x) = Tan 2x

So this is what I am doing

-2 Sin (3x + 7x)/2 Sin (3x-7x)/2

--------------------------------

2 Sin (3x + 7x)/2 Cos (3x-7x)/2

-2 Sin 5x Sin -2x

-----------------

2 Sin 5x Cos -2x

Sin 2x

-------

-cos 2x

Which equals -Tan 2x. What am i doing wrong??

Thanks