The roots of a quadratic equation $x^{2} = 49$ are ..... .

If the following quadratic equation has two equal and real roots,then find the value of $k$: $x(4 - kx) = 3 - 2x$.

The value of the discriminant $D$ of the quadratic equation $x^{2} + 5x + 1 = 0$ is $\ldots \ldots \ldots \ldots .$

If $81$ is the discriminant of $2x^{2} + 5x - k = 0$,then the value of $k$ is ..............

Find the discriminant of the following quadratic equation: $5x^{2} + 2x - 1 = 0$.

Verify whether the given value of $x$ is a solution of the quadratic equation or not: $4 \sqrt{3} x^{2} + 5 x - 2 \sqrt{3} = 0$; $x = \frac{\sqrt{3}}{4}$.