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factorising quadratics need help! :(

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    I've been stuck on this fact.quadratic for ages. I know what the real answer is but i can't get there this is the question and method:
    factorise 5x^2-17x-12=0
    -12x5=-60
    -20x3=-60 -20+3=-17
    (5x-20)(x+3)=0
    x=4 or x=-3

    the ACTUAL answer:
    x=4 or x=-3/5 how do i get to -3/5?? :confused:
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    5x^2-17x-12=0
    5x^2-20x+3x-12=0
    5x(x-4)+3(x-4)

    (x-4)(5x+3)=0

    x-4=0
    x=4

    5x+3=0
    5x=-3
    x=/3/5

    Hope this helps! Feel free to message me if you still don't understand
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    (Original post by Prada16)
    -20x3=-60 -20+3=-17
    (5x-20)(x+3)=0
    This is where you're going wrong, you will need to rewrite the equation as
    5x^2-20x+3x-12=0

    and then factorise it.
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    (Original post by lizz-ie)
    5x^2-17x-12=0
    5x^2-20x+3x-12=0
    5x(x-4)+3(x-4)

    (x-4)(5x+3)=0

    x-4=0
    x=4

    5x+3=0
    5x=-3
    x=/3/5

    Hope this helps! Feel free to message me if you still don't understand
    thanks i understand now

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Updated: June 8, 2012
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