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Thread: solving a equation

  1. #1
    Junior Member
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    Chelmsford, Essex, UK
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    solving a equation

    hi would I solve equations such as

    y=-3x+2

    and

    y=2x^2-7x-4

    by factorising or using the quad formula, as I need to find where the above intersect on a graph.

    Many thanks

    Dave
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  2. #2
    Senior Member
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    Sheffield England
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    Re: solving a equation

    Quote Originally Posted by davellew69 View Post
    hi would I solve equations such as

    y=-3x+2

    and

    y=2x^2-7x-4

    by factorising or using the quad formula, as I need to find where the above intersect on a graph.

    Many thanks

    Dave
    At intersection 2x^2-7x-4= -3x+2 So 2x^2 -4x -6=0 Divide both sides by 2 giving x^2-2x-3=0 Now factorize and get two values for x.
    Sub these back into y= -3x+2 to get the corresponding values of y.
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  3. #3
    Junior Member
    Joined
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    Re: solving a equation

    This is just a simple simultaneous equation. There will of course be 2 intersection points. $\displaystyle y=2x^2-7x-4$ is a parabola and $\displaystyle y=-3x+2$ will intersect it at 2 points.

    as $\displaystyle y=y$ then $\displaystyle 2x^2-7x-4=-3x+2$

    Therefore, $\displaystyle 2x^2-7x-4=-3x+2=2x^2-4x-6$

    $\displaystyle \frac{2x^2-4x-6}{2} = x^2-2x-3$

    This is a quadratic, so factorise this equation and it will give you two points for $\displaystyle x$. Put these back into the equation, and you will retrive the values for $\displaystyle y$.
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