Question13 Mark for Review
The function $f(x)=\frac{1}{9}(x-7)^{2}+3$ gives a metal ball's height above the ground $f(x)$, in inches, $x$ seconds after it started moving on a track, where $0 \leq x \leq 10$. Which of the following is the best interpretation of the vertex of the graph of $y=f(x)$ in the $x y$-plane? (A) The metal ball's minimum height was $\mathbf{3}$ inches above the ground. (B) The metal ball's minimum height was 7 inches above the ground. (C) The metal ball's height was 3 inches above the ground when it started moving. (D) The metal ball's height was 7 inches above the ground when it started moving.