The value of the discriminant of a quadratic equation $kx^{2} - 4x - 4 = 0$ is $64$,then $k = \dots$

The formula to find the sum $S$ of the first $n$ natural numbers is $S = \frac{n(n+1)}{2}$. Find $n$ if the sum of the first $n$ natural numbers is $300$.

If $b=0$ and $c < 0$,is it true that the roots of $x^{2}+bx+c=0$ are numerically equal and opposite in sign? Justify.

If the following quadratic equation has two equal and real roots,then find the value of $k$: $2kx^2 - 8x + k = 0$.

........ also mentioned a method to find the solution of quadratic equation.

If the value of the discriminant of a quadratic equation $kx^2 - 6x + 1 = 0$ is $0$,then $k = \ldots$