SOLUTION: Can you help me solve this identity? cos^(4)[theta]-sin^(4)[theta]=1-2sin^(2)[theta] I just don't understand this and would appreciate the help! =]

Question 290184: Can you help me solve this identity?
cos^(4)[theta]-sin^(4)[theta]=1-2sin^(2)[theta]
I just don't understand this and would appreciate the help! =]
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
cos^(4)[theta]-sin^(4)[theta]=1-2sin^(2)[theta]
Factor the left side.
Substitute for "1" on the right side:
------
(cos^2-sin^2)(cos^2+sin^2) = (cos^2 + sin^2) - 2sin^2
----
Since cos^2+sin^2 = 1 you get:
(cos^2-sin^2)(1) = cos^2-sin^2
cos^2-sin^2 = cos^2-sin^2
===============================
Cheers,
Stan H.

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