trig

If sin = 4/5 with A in QII, and sin B = -3/5 with B in QIV find cos(A-B)

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  1. cos(A-B)= cosAcosB+sinAsinB

    If sinA = 4/5 in QII
    draw you triangle in QII, and find the third side.
    The third side is 3. (Do the same thing for sin B= -3/5
    Plug in:
    cosAcosB-sinAsinB
    =(-3/5)*(4/5)+(4/5)*(-3/5)
    =(-12/25) -(-12/25)
    =-24/25

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  2. 53. the longest side is 55 cm. find the length of the shortest side

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