Hello,

I am trying to do the following question. I've just done a chapter which involved trig identities but apparently this one involves coordinate geometry though I'm not sure.

Using the identities in your notes, express the following in terms of the sines and cosines of x, y, 3x and 3y.

i) sin(3x - y)

ii) cos (x + 3y)

I realise this is probably a silly question but I just don't know how to go about it.

for the first one, I know that sin(theta) = -sin(-theta), but i'm not sure that is releavant. I also know that sin squared theta + cos squared theta = 1, but I don't know how to manipulate the equations I've been given or what they mean.

Any help at all is appreciated, many thanks in advance.