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    Right so, we're studying the discriminant zero equation and I plodded through the questions until I got to the last one.

    Here is it:

    Q) If a is negative and c is positive, what can be said about the graph of y = ax^2 + bx - c?

    The answer is that:

    The graph will bend upwards and intersect the x axis twice.

    I can kind of understand the answer but can't; I can see why it bends upwards since it is a positive x^2 graph but why does it intersect the x axis twice?

    Please could somebody explain, as nooby as this question is
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    its basically a U (an upside down parabola) so its intersects the x-axis twice as it is x^2 and as it is -c, then it will cross the y-axis at the negative bit
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    (Original post by Dededex)
    Right so, we're studying the discriminant zero equation and I plodded through the questions until I got to the last one.

    Here is it:

    Q) If a is negative and c is positive, what can be said about the graph of y = ax^2 + bx - c?

    The answer is that:

    The graph will bend upwards and intersect the x axis twice.

    I can kind of understand the answer but can't; I can see why it bends upwards since it is a positive x^2 graph but why does it intersect the x axis twice?

    Please could somebody explain, as nooby as this question is
    does it say anything about b??
    I would think you need to complete the square or consider the discriminant.
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    Because b^{2}-4ac is positive therefore it will intersect the graph twice.
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    (Original post by watchthis)
    its basically a U (an upside down parabola) so its intersects the x-axis twice as it is x^2 and as it is -c, then it will cross the y-axis at the negative bit
    wouldn't it be ∩-shaped?

    in the equation  D = \sqrt{b^2-4ac}
    since "c" = -c, D can never be less than b^2 which is larger than 0. So the equation y=0 always has 2 roots.
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    (Original post by Dededex)
    Right so, we're studying the discriminant zero equation and I plodded through the questions until I got to the last one.

    Here is it:

    Q) If a is negative and c is positive, what can be said about the graph of y = ax^2 + bx - c?

    The answer is that:

    The graph will bend upwards and intersect the x axis twice.

    I can kind of understand the answer but can't; I can see why it bends upwards since it is a negative x^2 graph but why does it intersect the x axis twice?

    Please could somebody explain, as nooby as this question is
    Fixed

    (And someone mentioned you can use the discriminant for it cutting the x axis twice)
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    (Original post by 808)
    wouldn't it be ∩-shaped?

    in the equation  D = \sqrt{b^2-4ac}
    since "c" = -c, D can never be less than b^2 which is larger than 0. So the equation y=0 always has 2 roots.
    yes, could be, but I always thought what determined whether the graph is a parabola or an upside down parabola was always whether ax^2 was positive or negative.

    yes, in fact it would be a parabola. my mistake as a is negative, didnt read the question ;p
 
 
 
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