completing the square
noun Mathematics.
a method, usually of solving quadratic equations, by which a quadratic expression, as x2 − 4x + 3, is written as the sum or difference of a perfect square and a constant, x2 − 4x + 4 + 3 − 4 = (x − 2)2 − 1, by addition and subtraction of appropriate constant terms.
Dictionary.com Unabridged
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019