<PRE><B>Question 1003504</B>
find the exact value of cos(a+b) if sin a =4/5 and sin b= -5/13 ( - in 5 only)with a in quadrant II and b in Quadrant III 
cos(a+b) = cos(a)cos(b)-sin(a)sin(b)
Since sin(a) = 4/5 in QII, cos(a) = -3/5
Since sin(b) = -5/13 in QIII, cos(b) = -12/13
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Substitute those values and solve for cos(a+b)
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Cheers,
Stan H.
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