## College Algebra (10th Edition)

number to be added: $4$ factored form: $(x-2)^2$
RECALL: To complete the square of an expression in the form $x^2-bx$, $(\frac{b}{a})^2$ must be added. The factored form of the result is $(x-\frac{b}{2})^2$. Thus, in the given expression add $(\frac{4}{2})^2=2^2=4$ to obtain: $x^2 -4x + 4$ Writing the square in factored form gives: $x^2-4x+4 = (x-2)^2$