Question

Determine an equivalent expression for sin 3x cos x + cos 3x sin x .
A. 4 sin x
B. 2 sin x cos x
C. 4 sin x cos x
D. 2 sin 2x cos 2x

Answer 1

D.
Just substitute x=1 in to the expressions and they should give the same as the expression.

Answer 2

sin3x cox+cos3x sinx
=sin(3x+x)
=sin(4x)
=sin(2x+2x)
=sin2x cos 2x+sin2x cos 2x
=2 sin2x cos 2x