AlgebraLab

Algebra I Recipe: Solving Quadratic Equations By Completing the Square

By G Redden

Steps to Solve
  1. Add or subtract to move the number term to the opposite side of x2 and x.
  2. If "a" > 1, divide both sides by "a". (Divide every term by "a".)
  3. Take half of "b", square it and add the value to both sides of the equation.
  4. Factor the perfect square trinomial on the left. Factors to look like (a ± b)2.
  5. Square root both sides of the equation to eliminate the "2". Give the positive and negative value of the right side.
  6. Solve for the variable.
1.
x2 + 10x – 11 = 0
2.
x2 - 8x + 12 = 0
3.
2x2 - 6x - 15 = 5
4.
5x2 - 20x – 20 = 5