Help! lol sin3q etc

[Monkey2009]

By writing sin3Q as Sin(2Q+Q)

showing that sin3Q=3sinQ-4sin3Q

Hey I have honestly no idea where to start with this any help will be appreciated. I know you are supposed to show what youve done but its one of these i dont even know where to start. if someone could explain many thanks

 

[skeeter]

\(\displaystyle \sin(2x+x) =\)

use the sum identity for sine ...

\(\displaystyle \sin(2x)\cos{x} + \cos(2x)\sin{x} =\)

use double angle identities ...

\(\displaystyle (2\sin{x}\cos{x})\cos{x} + (1-2\sin^2{x})\sin{x} =\)

\(\displaystyle 2\sin{x}\cos^2{x} + \sin{x} - 2\sin^3{x} =\)

\(\displaystyle 2\sin{x}(1 - \sin^2{x}) + \sin{x} - 2\sin^3{x}\)

you can clean up the algebra from this point.