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November 23, 2014

November 23, 2014

Posted by **Mitchel** on Sunday, February 17, 2013 at 11:33pm.

cos 4x + cos 2x = 2 - 2 sin^2(2x) - 2 sin^2 x

- Trig -
**Reiny**, Monday, February 18, 2013 at 12:32amusing the identity

cos 2A = cos^2 A - sin^2 A = 1 - 2sin^2 x = 2cos^2 x -1

LS = cos 4x + cos 2x

= cos^2 2x - sin^2 2x + cos 2x

= (1 - sin^2 (2x) ) - sin^2 (2x) + (1 - 2sin^2 x)

= 1 - 2sin^2 (2x) + 1 - 2sin^2 x

= 2 - 2sin^2 (2x) - 2sin^2 x

= RS

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