Question

Which expression does (sin x)(cos 2x) + (cos x)(sin 2x) simplify to?

a- cos 3x
b- -sin x
c- sin 3x
d- cos(-3x)

Answer 1

The correct answer is the third choice.

Explanation:

According to trigonometric identities, the given expression is equivalent to the sine of the sum of the angles involved.

In this case those angles are x and 2x. It means that the expression is sin(x+2x) which is the same as sin(3x).