document.write( "Question 1060407: Use a sum or difference formula to find the exact value of the following.
\n" ); document.write( "cos 2(pi)/5 cos(pi)/15 + sin2(pi)/5 sin(pi)/15 \n" ); document.write( "

Algebra.Com's Answer #675393 by ikleyn(52782) $\"\"$ $\"About$

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document.write( " =  =  =  =  = .\r\n" );
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document.write( "The sum or difference formulas for cosine are\r\n" );
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document.write( "cos(a+b) = cos(a)*cos(b) - sin(a)*sin(b),\r\n" );
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document.write( "cos(a-b) = cos(a)*cos(b) + sin(a)*sin(b).\r\n" );
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