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    I'm given a triangle, there are 2 known sides and I have to find the included angle

    I've labelled the angle as "C" and the known sides as "a" and "b"

    I am given the area [scroll to bottom of post to see values]

    I was wondering if there is a way to rearrange the formula of A= 1/2absinC so I could work out what "C" is. I've tried this but no lucl :'(

    Is there another way to work out this question??

    thanks^^

    a = 13cm
    b = 11cm

    Area = 67.2cm (squared)
    Show that angle C = 70.0 degrees
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    yes, you can rearrange it...
    multiply both sides by 2
    then divide both by ab
    you should then have an expression for sin C, use your calulator's sin^-1 function to work out C.
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    (Original post by Freeze123)
    I'm given a triangle, there are 2 known sides and I have to find the included angle

    I've labelled the angle as "C" and the known sides as "a" and "b"

    I am given the area [scroll to bottom of post to see values]

    I was wondering if there is a way to rearrange the formula of A= 1/2absinC so I could work out what "C" is. I've tried this but no lucl :'(

    Is there another way to work out this question??

    thanks^^

    a = 13cm
    b = 11cm

    Area = 67.2cm (squared)
    Show that angle C = 70.0 degrees
    You could make sin*C the subject, but it is often easier to simply insert the values in the correct locations and then solve.
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    A = \frac {absinC}{2}

    2A = absinC

    sinC = \frac {2A}{ab}

    C = sin^{-1}(\frac {2A}{ab})
 
 
 
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Updated: January 17, 2010
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