Posted by anonymous on Tuesday, May 25, 2010 at 1:02am.
It looks like you are working with the expansions of
sin 2A and cos 2A, and are expected to know those formulas
1. is a direct result of the expansion of
cos 2A = cos^2 A - sin^2 A
so cos^2(x/2)-sin^2(x/2) = cosx
2. again, direct application
2cos^2(3A)-1 = cos 6A
3. sin 2x/1+cos2x
= 2sinxcosx/(1 + cos^2 x - sin^2 x)
= 2sinxcosx(cos^2 x + cos^2 x)
= 2sinxcosx/(2cos^2 x)
= sinx/cosx
= tanx
You had tan 2x
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