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Math Help - Law of cosine

  1. #1
    Newbie
    Joined
    Apr 2009
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    14

    Law of cosine



    My teacher got 7.30, but I can't seem to get the right anwser.

    How do I solve for a?

    I get 14 when I solve it

    a^2=11^2+7^2-2(11)(7)cos62
    a^2=121+49-2(77)cos62
    a^2=270-154cos62
    a^2=197.70
    square root of a^2 = Square root of 197.70
    a=14.06
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  2. #2
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    Hello, live504!

    I don't agree with either of you . . .


    My teacher got 7.30, but I can't seem to get the right answer.

    I get 14 when I solve it

    a^2 \:=\:11^2+7^2-2(11)(7)\cos62

    a^2\:=\:121+49-2(77)\cos62

    a^2\:=\:{\color{red}270}-154\cos62\quad\hdots\quad {\color{blue}121 + 49 \:=\:170}

    a^2\:=\:197.70

    a \:=\:\sqrt{197.7} \;\approx\;14.06

    a^2 \;=\;170 - 154\cos62^o \;\approx\;97.70

    Therefore: . a \;=\;\sqrt{97.70} \;\approx\;9.88

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