document.write( "Question 375189: if cosA=3/5 what is the value of cos3A? \n" ); document.write( "

Algebra.Com's Answer #266841 by robertb(5830) $\"\"$ $\"About$

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$\"cos3A+=+cos%282A+%2B+A%29+=+cos2AcosA+-+sin2AsinA+\"$
\n" ); document.write( "= $\"%282%28cosA%29%5E2-1%29cosA+-+2sinAcosAsinA+=+2%28cosA%29%5E3-cosA+-+2%28sinA%29%5E2cosA\"$
\n" ); document.write( " = $\"+2%28cosA%29%5E3-cosA+-2%281-%28cosA%29%5E2%29cosA+=+4%28cosA%29%5E3+-+3cosA\"$ .
\n" ); document.write( "Then $\"cos3A+=+4%283%2F5%29%5E3+-+3%2A%283%2F5%29=+-0.936\"$ \n" ); document.write( "

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