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Math Help - Help with trigo qn

  1. #1
    Member maybeline9216's Avatar
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    Help with trigo qn

    Can anyone tell me whether angle A is acute or obtuse.Thanks...and help me with the qn too...i got a different answer.
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  2. #2
    MHF Contributor
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    cscA = 5/3, where 90deg < A < 180deg

    csc = hyp /opp

    So A is in the 2nd quadrant.
    The reference triangle of A has:
    opposite side = 3
    adjacent side = -4 ----------you know how to get this?
    hypotenuse = 5
    hence,
    tanA = opp/adj = 3 /(-4) = -3/4

    ---
    cosB = 5/13, where -90deg < B < 0deg

    cos = adj /hyp

    So, B is the 4th quadrant.
    The reference right triangle of B has:
    opp = -12 -----how about this?
    adj = 5
    hyp = 13
    hence,
    tanB = -12/5

    Then,
    tan(A +B)
    = [tanA +tanB] / [ 1 -tanAtanB]
    = [-3/4 -12/5] / [ 1 -(-3/4)(-12/5)]
    = 63/16 ------------------------------answer.
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  3. #3
    Member maybeline9216's Avatar
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    O.o no wonder i got it wrong... i wrote -4 become 4!!!
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