Math Playground
Algebra

Completing the square

Rewrite ax² + bx + c into a(x − h)² + k — and solve any quadratic.

Rewrite ax² + bx + c as a(x − h)² + k. The vertex is at (h, k) — and you can solve any quadratic.

Try it

x² + 6x + 5

Half of 6 is 3. (x+3)² = x² + 6x + 9. So x² + 6x + 5 = (x+3)² − 4.