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

Find the roots of the following quadratic equations by the factorisation method:
$\frac{2}{5} x^{2}-x-\frac{3}{5}=0$

The product of the digits of a two-digit number is $14$. The number obtained by interchanging the digits is $45$ more than the original number. Find the original number.

Which of the following polynomials does not have any real zero?

Find the roots of the following quadratic equation by the method of completing the square: $2x^{2} - 7x + 3 = 0$.

Find the roots of the following quadratic equation by the factorisation method:
$21 x^{2}-2 x+\frac{1}{21}=0$