Completing the Square

Completion of the square is the name given to a method of factorization of the polynomials due to this degree. Factoring takes its name from the fact that the factored form obtained owns the variable in a squared expression.

dCode can complete the square by depressing a polynomial expression

Consider \( x^2 +bx + c = 0 \) and add \( (b/2)^2 - c - (b/2)^2 + c (= 0) \) that allows factorizing in $$ (x +(b/2))^2 - (b/2)^2 + c $$

Example: Consider \( p(x)=2x^2+12x+14 \), in order to complete the square hand, factorize the coefficient of \( x^2 \) : \( p(x)=2(x^2+6x+7) \) and continue with \( q(x) = x^2+6x+7 \)

Example: Identify the coefficient of \( x \), here \( 6 \) and divide it by \( 2 \) to get \( β=6/2=3 \) and use \( β \) to write $$ q(x) = x^2 + 6x + 7 = (x+3)^2 − β^2 + 7 = (x+3)^2 − 2 $$

Example: Back to \( p(x) = 2q(x) \) to get the completed square: $$ p(x)=2x^2+12x+14=2((x+3)^2−2)=2(x+3)^2−6 $$

With the factorized form, it becomes simple to find the roots.

$$ p(x) = 0 \iff 2(x+3)^2−6 = 0 \iff (x+3)^2 = 3 \\ \iff x+3 = \pm \sqrt{3} \iff x = \pm \sqrt{3} - 3 $$

dCode can generalize the approach to other polynomials of order \( n \) superior to 2 by removing the term of degree \( n-1 \).