document.write( "Question 757630: Write the expression equivalent to cos 3 theta \n" ); document.write( "

Algebra.Com's Answer #460948 by pmatei(79) $\"\"$ $\"About$

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\n" ); document.write( "\n" ); document.write( " $\"cos%282%2Atheta%29+=+%28cos%28theta%29%29%5E2-%28sin%28theta%29%29%5E2\"$ \r
\n" ); document.write( "\n" ); document.write( " $\"sin%282%2Atheta%29+=+2+sin%28theta%29+cos%28theta%29\"$ \r
\n" ); document.write( "\n" ); document.write( "Replacing lines 2 and 3 into the first one and a bit of algebra:\r
\n" ); document.write( "\n" ); document.write( " $\"cos%283%2Atheta%29+=+%28cos%28theta%29%29%5E3-3+cos%28theta%29+%28sin%28theta%29%29%5E2\"$ \r
\n" ); document.write( "\n" ); document.write( "If you want only cosine functions replace $\"%28sin%28theta%29%29%5E2+=+1-%28cos%28theta%29%29%5E2\"$ :\r
\n" ); document.write( "\n" ); document.write( " $\"cos%283%2Atheta%29+=+4+%28cos%28theta%29%29%5E3+-+3+cos%28theta%29\"$ \n" ); document.write( "

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