document.write( "Question 1027182: cos(-x)cos x - sin (-x) sin x \n" ); document.write( "

Algebra.Com's Answer #642486 by ikleyn(52803) $\"\"$ $\"About$

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\n" ); document.write( "cos(-x)*cos(x) - sin(-x)*sin(x)
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document.write( "One way to find its value is\r\n" );
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document.write( "cos(-x)*cos(x) - sin(-x)*sin(x) =  = 1.\r\n" );
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document.write( "(On the way I used  cos(-x) = cos(x)  and  sin(-x) = -sin(x)).\r\n" );
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document.write( "The other way is to use the addition formula of trigonometry for cosines,\r\n" );
document.write( "which is   = .\r\n" );
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document.write( "When you use it with  = -x  and   = x,  you will get\r\n" );
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document.write( "cos(-x)*cos(x) - sin(-x)*sin(x) = cos((-x) + x) = cos(0) = 1.\r\n" );
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document.write( "Both ways lead to the same result.\r\n" );
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