A quadratic equation is an equation that can be rearranged in standard form as ax^2 + bx + c = 0, where x represents an unknown, and a, b, and c represent known numbers, where a is not equal to zero. If a is equal to zero, the equation is linear, not quadratic, as there is no ax^2 term. The numbers a, b, and c are coefficients of the equation and may be distinguished by calling them. As the below algorithm suggests, the values of x that satisfy the equation are called solutions of the equation and roots or zeros of the expression on its left-hand side. A quadratic equation has at most two solutions. If there is no real solution, there are two complex solutions.