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Thread: trigo help

  1. #1
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    trigo help

    Let angleA B C be angles of a triagnle ABC

    if $\displaystyle cos^2\frac{B}{2}+cos^2\frac{C}{2}+cosA=3/2$

    and $\displaystyle sinC + sinB = xsinA$

    then find the value of $\displaystyle x$
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  2. #2
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    Hello banku12
    Quote Originally Posted by banku12 View Post
    Let angleA B C be angles of a triagnle ABC

    if $\displaystyle cos^2\frac{B}{2}+cos^2\frac{C}{2}+cosA=3/2$

    and $\displaystyle sinC + sinB = xsinA$

    then find the value of $\displaystyle x$
    Are you sure you have this question correct?

    I assume that $\displaystyle x$ is supposed to have a constant value, but my spreadsheet calculations show that this is not so. For example:
    $\displaystyle B = 40^o$ gives $\displaystyle C = 32.16462...^o, A = 107.83538^o$ and $\displaystyle x = 1.234469$
    whereas
    $\displaystyle B = 60^o$ gives $\displaystyle C = 16.7785^o, A = 103.2214^o$ and $\displaystyle x = 1.18614$
    Check the question again, please.

    Grandad
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  3. #3
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    yes i am sure thats what is given in the question
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  4. #4
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    Hello banku12
    Quote Originally Posted by banku12 View Post
    yes i am sure thats what is given in the question
    Sorry, but the question is simply wrong, if $\displaystyle x$ is supposed to have constant value.

    Here's the Excel spreadsheet showing the calculations (with a slight improvement on the value of C in the second one).

    Grandad

    (In case you don't have Excel, I've attached a screen-shot as well.)
    Attached Thumbnails Attached Thumbnails trigo help-trigquestion.jpg  
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