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maths question - leaving cert algebra

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  • 25-10-2004 7:40pm
    #1
    ublinina
    Closed Accounts Posts: 21 ✭


    Can anybody help with this leaving cert maths question. its algebra part c .

    The quadratic equation f(x) = ax^2+ bx +c is shown , where a>0 ( a diagram of a quadratic curve is shown with the curve touching the x axis at point p ).

    The curve touches the x-axis at the point p.

    Find the co-ordinates of the point p in terms of a and b


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    #2
    Young Siward
    Closed Accounts Posts: 141 ✭✭Young Siward


    Hi,

    First of all i'm probably competely wrong here....

    First of all if the graph touches at one point only, then there's only one root.
    So b^2-4ac=0.
    therefore....b^2=4ac

    With this in mind, you can sub this into the quadratic formula to get x, this cancels out the square root part so you get (-b)/2a for x.

    So your answer should be (-b/2a,0)!

    I'm well rusty at this stuff, someone else?


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    #3
    DS
    Registered Users Posts: 654 ✭✭✭DS


    Yeah that's right.
    f(x) = 0 at x = p
    f(p) = 0
    ap^2 + bp + c = 0
    Use -b formula. You know there's only one value of x so b^2 - 4ac must = 0. That leaves you with -b/2a. Obviously the y coordinate is 0.


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    #4
    bp_me
    Registered Users Posts: 1,648 ✭✭✭bp_me


    What year was the question? All the solutions are available online - http://www.education.ie.


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    #5
    ublinina
    Closed Accounts Posts: 21 ✭ublinina


    Thanks for the help
    That seems to be the correct answer.
    (-b/2a)..


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