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If $2$ is a root of the quadratic equation $3x^2 + px - 8 = 0$ and the quadratic equation $4x^2 - 2px + k = 0$ has equal roots, find the value of k.
Given:
$2$ is a root of the quadratic equation $3x^2 + px -8 = 0$ and the quadratic equation $4x^2 -2px + k = 0$ has equal roots.
To do:
We have to find the value of k.
Solution:
If $m$ is a root of the quadratic equation $ax^2+bx+c=0$ then it satisfies the given equation.
Therefore,
$3x^2 + px -8 = 0$
$3(2)^2 + p(2) -8 = 0$
$3(4)+2p-8=0$
$12+2p-8=0$
$4=2p$
$p=\frac{4}{2}$
$p=2$
Substituting the value of $p$ in $4x^2 -2px + k = 0$, we get,
$4x^2 - 2(2)x + k = 0$
$4x^2-4x+k=0$
Comparing the quadratic equation $4x^2-4x+k=0$ with the standard form of a quadratic equation $ax^2+bx+c=0$,
$a=4, b=-4$ and $c=k$
The discriminant of the standard form of the quadratic equation $ax^2+bx+c=0$ is $D=b^2-4ac$.
$D=(-4)^2-4(4)(k)$
$D=16-16k$
The given quadratic equation has equal roots if $D=0$.
Therefore,
$16-16k=0$
$16=16k$
$k=\frac{16}{16}$
$k=1$
The value of $k$ is $1$.