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Math Help - Ugh, More Trig Stuff

  1. #1
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    Ugh, More Trig Stuff

    Another question i had was: If sin(alpha)=4/5 in quadrant 1 and
    cos(beta)=-11/12 in quadrant II, find

    Sin(alpha+beta)

    Tan(alpha+beta)

    Thats a LOT for the help.
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  2. #2
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    Quote Originally Posted by aussiekid90
    Another question i had was: If sin(alpha)=4/5 in quadrant 1 and
    cos(beta)=-11/12 in quadrant II, find

    Sin(alpha+beta)

    Tan(alpha+beta)

    Thats a LOT for the help.
    You could get fancy and use the sum of angles formulas, but I think it's easier just to find alpha and beta:
    \alpha = sin^{-1} \left ( \frac{4}{5} \right ) \approx 0.927295 \, rad
    \alpha is supposed to be 1st quadrant and, in fact, it is.

    \beta = cos^{-1} \left ( - \frac{11}{12} \right ) \approx  2.73045 \, rad
    which checks out as being in the 2nd quadrant.

    So:
    sin(\alpha + \beta) = sin(3.65775)=-0.493542
    tan(\alpha + \beta) = tan(3.65775) = 0.567471

    -Dan
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