Summary: Quadratic Equations

Key Concepts

  • Many quadratic equations can be solved by factoring when the equation has a leading coefficient of 1 or if the equation is a difference of squares. The zero-factor property is then used to find solutions.
  • Many quadratic equations with a leading coefficient other than 1 can be solved by factoring using the grouping method.
  • Another method for solving quadratics is the square root property. The variable is squared. We isolate the squared term and take the square root of both sides of the equation. The solution will yield a positive and negative solution.
  • Completing the square is a method of solving quadratic equations when the equation cannot be factored.
  • A highly dependable method for solving quadratic equations is the quadratic formula based on the coefficients and the constant term in the equation.
  • The discriminant is used to indicate the nature of the solutions that the quadratic equation will yield: real or complex, rational or irrational, and how many of each.
  • The Pythagorean Theorem, among the most famous theorems in history, is used to solve right-triangle problems and has applications in numerous fields. Solving for the length of one side of a right triangle requires solving a quadratic equation.


completing the square
a process for solving quadratic equations in which terms are added to or subtracted from both sides of the equation in order to make one side a perfect square
the expression under the radical in the quadratic formula that indicates the nature of the solutions, real or complex, rational or irrational, single or double roots.
Pythagorean Theorem
a theorem that states the relationship among the lengths of the sides of a right triangle, used to solve right triangle problems
quadratic equation
an equation containing a second-degree polynomial; can be solved using multiple methods
quadratic formula
a formula that will solve all quadratic equations
square root property
one of the methods used to solve a quadratic equation in which the [latex]{x}^{2}[/latex] term is isolated so that the square root of both sides of the equation can be taken to solve for x
zero-product property
the property that formally states that multiplication by zero is zero so that each factor of a quadratic equation can be set equal to zero to solve equations