## Calculus (3rd Edition)

The value of $(x+3)^{2}$ can be 0 (when x= -3) or positive. 0 is the smallest possible value of $(x+3)^{2}$. The minimum value of f(x) is attained when the value of $(x+3)^{2}$ is minimum, that is, 0. In that case, f(x)= 0-4=-4.