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August 2, 2015

Homework Help: Math - Trig - Double Angles

Posted by Anonymous on Saturday, November 17, 2007 at 5:37pm.

Prove:
sin2x / 1 - cos2x = cotx


My Attempt:
LS:
= 2sinxcosx / - 1 - (1 - 2sin^2x)
= 2sinxcosx / - 1 + 2sin^2x
= cosx / sinx - 1
= cosx / sinx - 1/1
= cosx / sinx - sinx / sinx


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Prove:
2sin(x+y)sin(x-y) = cos2y - cos2x

My Attempt:
RS:
= 1 - 2sin^2y - 1 - 2sin^2x
= 1 - 1 - 2sin^2y - 2sin^2x
= -2sin^2y - 2sin^2x

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