document.write( "Question 1042158: Hi i have to solve this problem, thanks for help.\r
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Algebra.Com's Answer #657106 by ikleyn(52797) $\"\"$ $\"About$

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\n" ); document.write( "Hi i have to solve this problem, thanks for help.\r
\n" ); document.write( "\n" ); document.write( "Sin^4x - Cos^4x = Sin^2x - Cos^2x
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document.write( "Are you familiar with this identity:  = {a+b)*(a-b)?\r\n" );
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document.write( "If not, or if you are not sure, look into the lesson The difference of squares formula in this site.\r\n" );
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document.write( "OK. Now, apply this identity to the left side. You will get\r\n" );
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document.write( " = .\r\n" );
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document.write( "But the first parentheses,   is equal to 1, as everybody knows.\r\n" );
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document.write( "Therefore, \r\n" );
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document.write( " = .\r\n" );
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document.write( "QED.\r\n" );
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