Trig
posted by Anonymous .
Find cos(s+t) if cos s= 1/2 and sin t= 3/5, s and t are in quadrant II.
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!

the first one is correct, for the second I got
(2√8 + √5)/9
or
(4√2 + √5)/9