document.write( "Question 766371: cos^4a+cos^2a=1 ,prove is it identity or not,thanks and regards \n" ); document.write( "

Algebra.Com's Answer #467308 by tommyt3rd(5050) $\"\"$ $\"About$

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not an identity:
\n" ); document.write( "To disprove an identity we need only a single exception:\r
\n" ); document.write( "\n" ); document.write( " $\"%0D%0Acos%5E4%28pi%29%2Bcos%5E2%28pi%29=%28-1%29%5E4%2B%28-1%29%5E2=2%0D%0A\"$ \r
\n" ); document.write( "\n" ); document.write( "and not 1\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( ":) \n" ); document.write( "

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