document.write( "Question 942867: Verify the identity. Be sure to show each step.\r
\n" ); document.write( "\n" ); document.write( "cos(x + y) + cos(x - y) = 2 cos x cos y \n" ); document.write( "
Algebra.Com's Answer #574823 by TimothyLamb(4379)\"\" \"About 
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trigonometric identities:
\n" ); document.write( "cosine of sum, cosine of difference:
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\n" ); document.write( "cos(x + y) = cosx cosy - sinx siny
\n" ); document.write( "cos(x - y) = cosx cosy + sinx siny
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\n" ); document.write( "cos(x + y) + cos(x - y) = cosx cosy - sinx siny + cosx cosy + sinx siny
\n" ); document.write( "cos(x + y) + cos(x - y) = cosx cosy + cosx cosy - sinx siny + sinx siny
\n" ); document.write( "cos(x + y) + cos(x - y) = cosx cosy + cosx cosy + 0
\n" ); document.write( "cos(x + y) + cos(x - y) = 2 cosx cosy
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