Find cos(s+t) if cos s= -1/2 and sin t= 3/5, s and t are in quadrant II.

Question

I got the answer to be -4/10 plus -3sqrt(3)/10. Is that right?

Then a second problem was find sin (s+t) if sin s=2/3 and sin t=-1/3, sin is in quadrant II and t in quadrant IV. I got answer of 2sqrt(8/9) plus -sqrt(5)/9.

Can someone tell me if I did these right because I have a test tomorrow tahnks!

Answer 1

the first one is correct, for the second I got

(2√8 + √5)/9
or
(4√2 + √5)/9