Don’t be fooled: Not all quadratic equations can be solved by factoring. For example, x² - 3x = 3 is not solvable with this method. One way to solve quadratic equations is by completing the square; still another method is to graph the solution (a quadratic graph forms a parabola—a U-shaped line seen on the graph). But one of the most well-known ways is by using the quadratic formula (see below).

For example, if we want to find the roots of the polynomial x² + 2x - 7, we can replace the “corresponding” numbers from the initial equation into the quadratic equation; thus, a = 1, b = 2, and c = -7. Substituting these numbers into the quadratic formula, we solve for:

That equals