document.write( "Question 1141650: Verify the following identity by using an angle sum identity: cos (2x) = 1 - 2(sin2 x). Hint (2x = x + x) \n" ); document.write( "

Algebra.Com's Answer #762232 by ikleyn(52806) $\"\"$ $\"About$

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document.write( "First step is to write the basic formula correctly:\r\n" );
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document.write( "    cos(2x) = 1 - 2*sin^2(x).\r\n" );
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document.write( "    //  In your post the formula is presented by incorrect way !\r\n" );
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document.write( "Second step is verification\r\n" );
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document.write( "    cos(2x) = cos(x+x) = cos(x)*cos(x) - sin(x)*sin(x) = cos^2(x) - sin^2(x) = (1-sin^2(x)) - sin^2(x) = 1 - 2*sin^2(x).\r\n" );
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document.write( "QED.\r\n" );
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