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

1 Answer
Feb 22, 2016

First rearrange the equation into standard form, #x^2-4x-21=0#. The discriminant is then #(-4)^2-4*1*(-21)=16+84=100#. Given that the discriminant is positive, there are two real roots.


Standard form for a quadratic equation is #ax^2+bx+c=0#.

Once the equation has been arranged in this form, the discriminant is given by #b^2-4ac#.

If the discriminant is positive there are two real roots, if it is negative there are two imaginary roots, if it is zero there is one real root.