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

1 Answer
David G.
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.

Explanation:

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.

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