# trig

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how do you work find sin (a-B)beta sign. sin a = 12/13,a lies in quadrant II,and cos B = 15/17, B lies in quadrant I.

• trig -

Can't quite figure out some of the verbage, but

if A is in QII and sinA = 12/13, the cosA = -5/13

if B is in QI and cosB = 15/17, then sinB = 8/17

So,

sin(A-B) = sinAcosB - cosAsinB
= (12/13)(15/17) - (-5/13)(8/17)
= 180/221 + 40/221 = 220/221

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