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Math Help - Find the Missing parst of the Triangle Using the Laws of Cosines

  1. #1
    Junior Member Jarod_C's Avatar
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    Find the Missing parst of the Triangle Using the Laws of Cosines

    Hey people. Here's the question.

    Find the missing parts of the triangle by using the laws of cosines.
    What's known is, B=27, a=11, c=22

    Solving for b,
    b^2=11^2+22^2-2(11)(22)(cosB)
    b^2=121+484-2(242)(.891)
    b^2=605-432
    b^2=\sqrt{173}
    b=13.2

    Solving for A
    \frac{11}{sinA}=\frac{13.2}{sin27}

    Cross multiply.
    \frac {sin27\cdot 11}{13.2}=.3783(sin^-^1)=~22

    Solving for C

    \frac{22\cdot sin27}{13.2}=.7567(sin^-^1)=~49


    180-27-49-22=82? Where did I go so wrong. This formula has always seemed to work for me.
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  2. #2
    Super Member
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    Re: Find the Missing parst of the Triangle Using the Laws of Cosines

    But you have been asked tom use cosine formula and that it
    cos A = [b^2 + c^2 - a^2 ]/ 2 bc
    cos B = [c^2 + a^2 - b^2 ]/ 2 ac
    cos C = [a^2 + b^2 - c^2 ]/ 2 ab
    Use these expressions to get the result.
    Thanks from Jarod_C
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  3. #3
    Junior Member Jarod_C's Avatar
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    Re: Find the Missing parst of the Triangle Using the Laws of Cosines

    Have you ever noticed there are 3 steps when using this forum. 1 post a question, 2 wait for answer 3 get answer then feel stupid. hahaha

    Thanks, that solved it.
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