document.write( "Question 371826: Verify the identity (cos t+cos4t+cos7t) / (sin t+sin4t+sin7t)=cot4t \n" ); document.write( "

Algebra.Com's Answer #264861 by robertb(5830) $\"\"$ $\"About$

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cos t+cos4t+cos7t = -2cos4tcos3t + cos4t = cos4t(1-2cos3t), by using $\"-2cos%28%28A%2BB%29%2F2%29cos%28%28A-B%29%2F2%29+=+cosA+%2B+cosB\"$ .
\n" ); document.write( "Similarly,
\n" ); document.write( "sin t+sin4t+sin7t = -2sin4tcos3t + sin4t = sin4t(1-2cos3t), using $\"2sin%28%28A%2BB%29%2F2%29cos%28%28A-B%29%2F2%29+=+sinA+%2B+sinB\"$ . Therefore
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