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    When I'm asked let's say find k from a quadratic equation .
    I have to find the set of possible value of knursing discriminats, my question is when you find the discfimant of the quadratic equation with the k the constant I'm left with a quadratic what does it represent ? Is it y value or x?

    I.e. k^2-4k-12 -----> (k-6)(k+2) so k is either -2 or 6 what does this show?
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    (Original post by FrostedStarzzz)
    When I'm asked let's say find k from a quadratic equation .
    I have to find the set of possible value of knursing discriminats, my question is when you find the discfimant of the quadratic equation with the k the constant I'm left with a quadratic what does it represent ? Is it y value or x?

    I.e. k^2-4k-12 -----> (k-6)(k+2) so k is either -2 or 6 what does this show?
    Er... I THINK I know what you're asking...

    The typical question would be "Find the values of k for which the equation x^2+kx+(k+3)=0 has no real roots"

    Then you know that for no real roots you need to have b^2-4ac < 0 so k^2-4(k+3)<0. This equation represents a condition on k, with which the above quadratic has no real roots. You want to simplify this condition down into something like k<a or something. So we have k^2-4k-12=(k-6)(k+2)<0 and now you can draw this separate parabola in k on a different axis, say the ky axis, and observe for what values of k this equation is below the y-axis. The roots of this quadratic in k are important because that's where the quadratic goes from being +ve to -ve.

    So sketching this you'd find that the graph dips below y=0 in the region -2<k<6 and this is the simplified condition the question wants to see.


    In your example, I dunno what quadratic you started off with, but I assume the question was to find the values of k for which it has equal roots. So you found your b^2-4ac=0 to be k^2-4k-12=0 \Rightarrow (k-6)(k+2)=0 so k=6 or k=-2 and these represent conditions again on k for which the discriminant of the quadratic =0 which implies that the quadratic has equal roots.
 
 
 
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