en.wikipedia.org/wiki/Completing_the_square

In elementary algebra, completing the square is a technique for converting a quadratic polynomial of the form. a x 2 + b x + c {\displaystyle ax^{2}+bx+c} ...

www.mathsisfun.com/algebra/completing-square.html

But if you have time, let me show you how to "Complete the Square" yourself. Completing the Square. Say we have a simple expression like x2 + bx. Having x ...

www.khanacademy.org/math/algebra/quadratics/solving-quadratics-by-completing-the-square/v/solving-quadratic-equations-by-completing-the-square

For example, x²+6x+5 isn't a perfect square, but if we add 4 we get (x+3)². This, in essence, is the method of *completing the square*. Created by Sal Khan, ...

www.khanacademy.org/math/algebra/quadratics/solving-quadratics-by-completing-the-square/a/solving-quadratic-equations-by-completing-the-square

For example, solve x²+6x=-2 by manipulating it into (x+3)²=7 and then taking the square root.

www.purplemath.com/modules/sqrquad.htm

Demonstrates, with step-by-step instructions and illustrations, how to complete the square to solve a quadratic equation.

www.virtualnerd.com/algebra-1/quadratic-equations-functions/completing-the-square/completing-the-square-solutions/completing-the-square-solution-example

www.wyzant.com/resources/lessons/math/algebra/completing-the-square

When the highest exponent of an equation is 2, the method of "Completing the Square" gives us an alternative. This method will help us turn this unfactorable ...