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July 2, 2015

Homework Help: Math - Trig - Double Angles

Posted by Anonymous on Saturday, November 17, 2007 at 6:17pm.

Prove:
cos4x = 8cos^4x - 8cos^2x + 1

My Attempt:
RS:
= 4cos^2x (2cos^2x - 1) + 1
= 4 cos^2x (cos2x) + 1

LS:
= cos2(2x)
= 2cos^2(2x) - 1
= (cos^2(2)) - cos^2(2x)) - 1





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Prove:
8cos^4x = cos4x + 4cos2x + 3

My Attempt:
RS:
= cos2(2x) + 4cos(2x) + 3
= 2cos^2(2x) - 1 + 2(4)cos^2(2x) - 1 + 3

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