Question

I have two more to show they are an identity.
sin (A+B)/sin(A-B)= -cot A + cot B/cot A-cot B
and
sin 4x = 4 sin x cos³x-4sin³xcosx

Answer 1

for the first one I've gotten as far as changing the left side to read:
sinA cosB+cosA sinB/sinA cosB-cosA sinB

Answer 2

second one:
\[sin(4x)=2sin(2x)cos(2x)\] this is the 'double angle' formula for sine thinking of 4x as 2*2x now use the double angle formulas again for sine and cosine and this should give it to you.