Trig identity

[thenewbosco]

no clue how to start this:

show

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

 

[Dr Avalanchez]

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

 

[thenewbosco]

right so after doing this i get

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

whats next

 

[Dr Avalanchez]

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

 

[thenewbosco]

thanks for the help i got this and the others