# Trig identity

## Main Question or Discussion Point

no clue how to start this:

show

sin 3x = 3 sin x - 4 sin^3 x

## Answers and Replies

How to start this: sin(3x) = sin(2x+x)

right so after doing this i get

sin 3x = sin2x(cos x) + (cos2x)(sin x)

whats next

sin(2x)=...?
cos(2x)=...?

thanks for the help i got this and the others