Friday

August 22, 2014

August 22, 2014

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

**Related Questions**

Pre-calc/Calc - Which expression is equivalent to sin(3x) + sin x? A. 2cos(2x)...

Math - Which expression is equivalent to sin(3x) + sin x? A) 2cos(2x)sin x B) ...

tigonometry - expres the following as sums and differences of sines or cosines ...

Calc - Which functions of x and y in terms of time t can be derived from this ...

Precal - I do not understand how to do this problem ((sin^3 A + cos^3 A)/(sin A...

Precalculus - Verify the identities. Cos^2x - sin^2x = 2cos^2x - 1 When ...

Math, derivatives - f(x) = x² + 2Cos²x, find f ' (x) a) 2(x+cos x) b) x - sin x ...

trigonometry (please double check this) - Solve the following trig equations. ...

Math - Solving Trig Equations - What am I doing wrong? Equation: sin2x = 2cos2x ...

Ap Calc AB - Determine (dy/dx) using implicit differentiation. cos(X^2Y^2) = x I...