SOLUTION: cos^4a+cos^2a=1 ,prove is it identity or not,thanks and regards

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Question 766371: cos^4a+cos^2a=1 ,prove is it identity or not,thanks and regards
Answer by tommyt3rd(5050) About Me  (Show Source):
You can put this solution on YOUR website!
not an identity:
To disprove an identity we need only a single exception:
%0D%0Acos%5E4%28pi%29%2Bcos%5E2%28pi%29=%28-1%29%5E4%2B%28-1%29%5E2=2%0D%0A
and not 1

:)