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Simple but amazingly hard quadratic- can't factorise! watch

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    I'm doing a workbook before my first ever maths lecture tomorrow, and I can't factorise this quadratic! :O

    x squared minus x minus 1

    The solution is (x-0.5(1-sqrt 5))(x-0.5(1+sqrt 5 ))

    Its driving me mad!

    I've never factorised a quadratic that has had a similar answer before, but I notice that it has something to do with taking advantage of:

    a^2 + b^2 = (a+b)(a-b)

    What is the method for solving these quadratics, and when do you know how to use this method?

    Thanks guys im in a bit of a jam here :/
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    (Original post by joelio36)
    I'm doing a workbook before my first ever maths lecture tomorrow, and I can't factorise this quadratic! :O

    x squared minus x minus 1

    The solution is (x-0.5(1-sqrt 5))(x-0.5(1+sqrt 5 ))

    Its driving me mad!

    I've never factorised a quadratic that has had a similar answer before, but I notice that it has something to do with taking advantage of:

    a^2 + b^2 = (a+b)(a-b)

    What is the method for solving these quadratics, and when do you know how to use this method?

    Thanks guys im in a bit of a jam here :/
    x^2-y^2=(x+y)(x-y) NB it is minus and not plus as you have written.

    Is it x^2-x-1=0
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    Use the quadratic formula after you have x(sqrt) - x - 1
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    PS Helper
    quadratic roots formula..
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    uh a^2-b^2=(a+b)(a-b)
    aka difference of two squares.

    For this example use the quadratic formula to find the roots and then you know that (x-r_1)(x-r_2) will give you your quadratic where r_n is a root.
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    Cheers guys i got it now
 
 
 
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Updated: October 9, 2009

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