Algebra 1 · Quadratic Functions
Completing the Square
Algebra 1 · Quadratic Functions
Definition
Completing the square is a method that rewrites a quadratic as a perfect square plus a constant.
Examples
- x^2 + 6x = (x + 3)^2 - 9.
- x^2 - 4x + 1 = (x - 2)^2 - 3.
Key rule
Add and subtract (b/2)^2 to form a perfect square.
Memory hook
Complete the square - add (b/2)^2 to build the square.