Pre-Calc Help!!!!!!!!

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Evaluate the expression under the given conditions.
sin (A+B); tan A= 12/5, A in quadrant 3, sin B= -3sqrt(10)/10, B in quadrant 4.

  • Pre-Calc Help!!!!!!!! -

    in QIII, sin and cos are both negative.
    You have a 5-12-13 triangle, so
    sinA = -12/13
    cosA = -5/13

    in QIV, cos is positive.
    You have a 3-1-√10 triangle, so
    cosB = 1/√10

    Now apply the addition formula

    sin(A+B) = sinAcosB + cosAsinB

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