# How do you find value of discriminant then describe number and type of solutions for x^2 - 21 = 4x?

First rearrange the equation into standard form, ${x}^{2} - 4 x - 21 = 0$. The discriminant is then ${\left(- 4\right)}^{2} - 4 \cdot 1 \cdot \left(- 21\right) = 16 + 84 = 100$. Given that the discriminant is positive, there are two real roots.
Standard form for a quadratic equation is $a {x}^{2} + b x + c = 0$.
Once the equation has been arranged in this form, the discriminant is given by ${b}^{2} - 4 a c$.