If both the roots of a quadratic equation $kx^{2} + 4x + 1 = 0$ are equal,then $k = \ldots$

The formula for finding the value of $D$ (discriminant) for a quadratic equation $ax^2 + bx + c = 0$ is $\ldots \ldots \ldots \ldots.$

If the following quadratic equation has two equal and real roots,then find the value of $k$: $x^{2}-(k+10)x+9(k+1)=0$.

Find the discriminant of the following quadratic equation and hence determine the nature of the roots of the equation: $x^{2} = 9$.

The quadratic equation $2x^{2} - \sqrt{5}x + 1 = 0$ has

Find the discriminant of the following quadratic equation: $x^{2}-7x+10=0$