MHB CraxyCat's Yahoo Answers Question

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The discriminant of the quadratic equation \(kx^2 - 4x + k\) is calculated as \(D = b^2 - 4ac\), resulting in \(D = 16 - 4k^2\). For the equation to have equal roots, the discriminant must equal zero, leading to the equation \(16 - 4k^2 = 0\). Solving this gives the possible values of \(k\) as \(k = \pm 2\). The discussion confirms the correctness of this solution. Thus, the values of \(k\) that allow for equal roots in the quadratic are \(k = 2\) and \(k = -2\).
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CrazyCat's Question:
"Find the discrimnant of \(kx^2 - 4x + k\) in terms of \(k\), hence find possible values of \(k\) given that \(kx^2 -4x + k = 0\) has equal roots."



Answer:
For a quadratic \(ax^2+bx+c\) the discriminant is \(b^2-4ac\) this is the term that appears under the square root sign in the quadratic formula:
\[x=\frac{-b\pm\sqrt{b^2-4ac} }{2a}\]for the solution of \(ax^2+bx+c=0\). The quadratic equation has equal roots precisely when the discriminant is zero.

Now for the problem at hand \(a=k\), \(b=-4\) and \(c=k\) so the discriminant is \(D=b^2-4ac=16-4k^2\), and when \(D=0\) we have \(16-4k^2=0\) which we may solve for \(k\) to find: \(k=\pm2\).

CB

 
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