how to prove?

(cot^2 x-1) / (2 cot x) = cot 2x

cos 3x = 4 cos^3 x-3 cosx

sin 2t+sin t/1+cos t+sos 2t = tan t

THANK YOU!

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- Feb 22nd 2009, 11:18 PMpongpongestablishing identities?
how to prove?

(cot^2 x-1) / (2 cot x) = cot 2x

cos 3x = 4 cos^3 x-3 cosx

sin 2t+sin t/1+cos t+sos 2t = tan t

THANK YOU! - Feb 22nd 2009, 11:46 PMmathaddict

Knowing the fact that cot x = 1/tan x . - Feb 22nd 2009, 11:56 PMmathaddict
- Feb 23rd 2009, 05:55 AMSoroban
Hello, pongpong!

The third one is impossible to read.

Well, not "impossible" . . . I figured it out!

Quote:

We're expected to know these Double-Angle Identities:

. . . . .

The left side becomes: .

Factor and reduce: .