Trig

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!

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  1. the first one is correct, for the second I got

    (2√8 + √5)/9
    or
    (4√2 + √5)/9

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    posted by Reiny

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