You may want to review solving quadratic equations first.

The bit of the quadratic formula inside the square root sign
— *b*^{2} − 4*ac* — is called
the *discriminant*. It tells you a lot about the equation
you're trying to solve. If it's positive, then the equation will
have two real solutions. If it's 0, then the equation will have
only one solution (which will be real), since 0 has only one
square root. If it's negative, then the equation will have two
non-real solutions.

Furthermore, if it's positive, then we can learn something about the two real solutions by looking more closely. If it's a square, then the two solutions will both be rational. If not, then they will both be irrational (but still real).