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    Hello, I'm having trouble with the following edexcel question:

    Find, as surds, the roots of the equation 2(x+1)(x-4)-(x-2)^2 = 0

    So to begin with you know it won't factorise, so you need to complete the square or stick it into the formula.

    2(x^2-3x-4)-x^2-4x+4 = 0
    2x^2 - 6x - 8 - x^2 - 4x + 4 = 0
    x^2 - 10x - 4 = 0

    I put it into the formula and get (10 +- sqrt(116))/2

    The answer should be 1 +- sqrt (13)

    I have no idea where I have gone wrong, I just tried to complete the square and got 5 +- sqrt(29)

    I'm so confused
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    (Original post by iron_lloyd)
    Hello, I'm having trouble with the following edexcel question:

    Find, as surds, the roots of the equation 2(x+1)(x-4)-(x-2)^2 = 0

    So to begin with you know it won't factorise, so you need to complete the square or stick it into the formula.

    2(x^2-3x-4)-(x^2-4x+4) = 0
    2x^2 - 6x - 8 - x^2 + 4x - 4 = 0


    I put it into the formula and get (10 +- sqrt(116))/2

    The answer should be 1 +- sqrt (13)

    I have no idea where I have gone wrong, I just tried to complete the square and got 5 +- sqrt(29)

    I'm so confused
    Try again from there.
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    2x2-6x-8-x2+4x-4=0
    x2-2x-12=0

    (x-1)2-12-1=0
    (x-1)2-13=0
    x-1=(sqr+-)13
    x=1(sqr+-)13
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    (Original post by gomc)
    2x2-6x-8-x2+4x-4=0
    x2-2x-12=0

    (x-1)2-12-1=0
    (x-1)2-13=0
    x-1=(sqr+-)13
    x=1(sqr+-)13
    There we go. It was just one silly mistake you'd made

    EDIT: Also, this isn't an inequality
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    (Original post by Andy98)
    Try again from there.
    Oh dear.

    x^2 - 2x - 12 = 0

    (x-1)^2 - 13 = 0 therefore x = 1+- sqrt(13)

    Thanks ever so much... I really must keep an eye out for that - before a squared bracket.

    Edit: Yeah this part of the question isn't xD the next part is an inequality though, I just read off the question ^^
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    (Original post by Andy98)
    There we go. It was just one silly mistake you'd made

    EDIT: Also, this isn't an inequality
    I hope you don't mind me asking another question but I have a feeling the answer is wrong in their answer sheet.

    You have to work out an area in the second part of a question to give you the equation:

    x(x-5)<104

    Which I got and was correct.

    It then asks you to calculate the values of x given the previous answer:

    x^2 - 5x - 104 < 0

    putting that into the formula equation I get (5+- sqrt 446)/2 which gives me x = 13 or x = -8

    In the answers x = 13 is correct however x = -8 is not, it should work out to be x=10.5


    If I managed to get x=13 correct off the same quadratic formula I don't see why I get the second part wrong ?

    Edit: I'm being really naive.. of course they haven't got the answers wrong!
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    (Original post by iron_lloyd)
    Oh dear.

    x^2 - 2x - 12 = 0

    (x-1)^2 - 13 = 0 therefore x = 1+- sqrt(13)

    Thanks ever so much... I really must keep an eye out for that - before a squared bracket.

    Edit: Yeah this part of the question isn't xD the next part is an inequality though, I just read off the question ^^
    Fair enough

    (Original post by iron_lloyd)
    I hope you don't mind me asking another question but I have a feeling the answer is wrong in their answer sheet.

    You have to work out an area in the second part of a question to give you the equation:

    x(x-5)<104

    Which I got and was correct.

    It then asks you to calculate the values of x given the previous answer:

    x^2 - 5x - 104 < 0

    putting that into the formula equation I get (5+- sqrt 446)/2 which gives me x = 13 or x = -8

    In the answers x = 13 is correct however x = -8 is not, it should work out to be x=10.5


    If I managed to get x=13 correct off the same quadratic formula I don't see why I get the second part wrong ?

    Edit: I'm being really naive.. of course they haven't got the answers wrong!
    You're not being naive - I got \frac{5\pm\sqrt{441}}{2}, which comes out as x=13 or x=-8
 
 
 
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