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If 1-cosA=5/13, prove that 25sinA(sinA - cosA)

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    if 1 - cosA = 5/13
    then cosA = 1-5/13 = 12/13

    A could be in I or IV
    For I:
    cosA = 12/13
    then sinA = 5/13

    25sinA(sinA-cosA_ = 25(5/13)(5/13 - 12/13)
    = ...

    for IV
    cosA = 12/13
    then sinA = -5/13

    25sinA(sinA - cosA)
    = 25(-5/13)(-5/13 - 12/13)
    = ....

    I will leave the arithmetic up to you

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