Thread: Proving Trigonometry Identities Help

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And also, I'm confused about this.. is -tanx-tanx equal to -2tanx or -tan2x?

This question shows you are not familiar with the subject. My advice is that you should read your textbook/notes again. Work out few simple problems.

By the way -tan x -tan x = -2 tan x

I will answer your question, but I doubt you will understand every step clearly. First read the identities and know them clearly and then re read my post, you will understand the solution.

Originally Posted by fayeorwhatsoever

Prove: sin squared 2x cos squared 2x=1/8 (1-cos8x)

For the first equality, I have used the relation

For the second equality I have used