SOLUTION: prove the following identity 1. cos^2 3x - cos6x = sin^2 3x find the general solution of: 2cos^2 x + cos2x + sin2x =0

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Question 1072510: prove the following identity
1. cos^2 3x - cos6x = sin^2 3x
find the general solution of:
2cos^2 x + cos2x + sin2x =0
Answer by ikleyn(52787) About Me  (Show Source):
You can put this solution on YOUR website!
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prove the following identity
1. cos^2 3x - cos6x = sin^2 3x
~~~~~~~~~~~~~~~~~~~~~~~~~~ 

Apply the formula cos(2a) = cos^2(a) - sin^2(a).

Take a = 3x. You will get

cos(6x) = cos^2(3x) - sin^2(3x), 

which is what has to be proved.