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February 1, 2015

February 1, 2015

Posted by **Chris** on Thursday, April 18, 2013 at 11:42am.

A.

2cos(2x)sin x

B.

2sin(2x)sin x

C.

-2sin(2x)cos x

D.

2sin(2x)cos x

E.

-2cos(2x)sin x

- Calc -
**Reiny**, Thursday, April 18, 2013 at 3:16pmI don't know if you came across the identity

sin (3x) = 3sinx - 4sin^3 x

so yours:

sin(3x) + sinx = 4sinx - 4sin^3 x

= 4sinx(1 - sin^2x)

= 4sinx(cos^2x)

= 2(2sinxcosx)(cox) --. I just grouped them

= 2(sin(2x) (cosx)

which is D

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