# Completing the Square

How to solve quadratic equations by completing the square: example and its solution.

## Example

Move the constant term -5 to the right side.

Change +8*x* to +2⋅*x*⋅4.

Write +4^{2} on both sides.

Factor the left side by using the formula:*x*^{2} + 2⋅*x*⋅4 + 4^{2} = (*x* + 4)^{2}.

Square root both sides.

Add ± in front of √21,

because both (√21)^{2} and (-√21)^{2} can be 21.

Move +4 to the right side.

Then *x* = -4 ± √21.