document.write( "Question 1169171: Use Demoivre's theorem to prove that tan4x=((4tanx-3tan^(2)x))/(1-6tan^(2)x+tan^(4)x) \n" ); document.write( "
Algebra.Com's Answer #794717 by AnlytcPhil(1807)\"\" \"About 
You can put this solution on YOUR website!
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document.write( "Is this what you mean?\r\n" );
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document.write( "If so, then this is not an identity.  For let x = 45°\r\n" );
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document.write( "\"tan%28180%5Eo%29+=+%284%281%29+-+3%281%29%5E2%29%2F%281+-+6%281%29+%2B+%281%29%5E4%29\"\r\n" );
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document.write( "\"0+=+%284+-+3%29%2F%281+-+6+%2B+1%29\"\r\n" );
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document.write( "\"0+=+1%2F%28-4%29\"\r\n" );
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document.write( "\"0=-1%2F4\"\r\n" );
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document.write( "That's false, so the equation is not an identity so we can't prove\r\n" );
document.write( "what's false is true!\r\n" );
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document.write( "Edwin
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