a) Write 3x as the sum of two terms involving x.

b) Substitute the expression from part a) into sin3x.

c) Use an appropriate compound angle formula to expand the expression from part b).

d) Use an appropriate double angle formula to expand any terms involving 2x in the expanded expression from part c). Simply as much as possible.

e) Select a value for x, and show that your expression in part d) holds true for that value. (use pi/3 for x)

What I've got so far

a) (2x+x)

b) sin(2x+x)

c) sin2xcosx + cos2xsinx

d) I'm a bit unsure of this one.

e) After I solve d) I sub in pi/3, remembering that sin pi = 0 and sin pi/3 = sqrt(3) / 2.

So pretty much D) is the only one im having trouble with, can anyone enlighten me on this? Thanks in advance!