from wikipedia
A quadratic equation with real or complex coefficients has two solutions, called roots. These two solutions may or may not be distinct, and they may or may not be real.
The roots are given by the quadratic formula
where the symbol "±" indicates that both
-
and 
are solutions of the quadratic equation.
There is also a shortened version of the quadratic formula which is commonly used when the coefficient of x is an even number:
In this case the solutions are given by:
