Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$\color{blue}{x^2+6x+9}$
RECALL: $(a+b)^2=a^2+2ab+b^2$ Use the formulal above to obtain: $(3+x)^2 \\=3^2+2(3)(x)+x^2 \\=9+6x+x^2 \\=\color{blue}{x^2+6x+9}$