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    In a triangle ABC, AB=(x-3)cm, BC=(x+3)cm, AC=8cm and angle BAC=60 degrees.Use the cosine rule to find the value of x?

    I keep getting an answer of 2 and the answer should be 4.4

    Help would be much appreciated..................... ...................
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    You sure the answer is 4.4? I get 4 :confused:
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    (Original post by vaider)
    In a triangle ABC, AB=(x-3)cm, BC=(x+3)cm, AC=8cm and angle BAC=60 degrees.Use the cosine rule to find the value of x?
    I keep getting an answer of 2 and the answer should be 4.4
    Help would be much appreciated..................... ...................
    a²=b²+c²-2bc.cos A
    (x+3)²=8²+(x-3)²-(2 x 8(x-3)cos 60)
    x²+3x+3x+9=64+x²-3x-3x+9-8x+24
    x²+6x+9 - x²-14x+97 = 20x-88
    20x=88
    x=4.4
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    (Original post by Lil_J)
    (x+3)²=8²+(x-3)²-(2 x 8(x+3)cos 60)
    Shouldn't that line be:
    (x+3)²=8²+(x-3)²-(2 x 8(x-3)cos 60) ?
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    Thanks for your help guys I think I was just getting confused with all the x's and numbers and couldn't manage to tidy them up!
 
 
 
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