Ans: C
Let $y = k_1 +k_2x^2$, where $k_1$ and $k_2$ are non-zero constants.
Let $y = k_1 +k_2x^2$, where $k_1$ and $k_2$ are non-zero constants.
When $x=1$, $y=7$. We have
$\begin{array}{rcl}
7 & = & k_1 + k_2(1)^2 \\
k_1 + k_2 & = & 7 \ \ldots \unicode{x2460}
\end{array}$
When $x=2$, $y=13$. We have
$\begin{array}{rcl}
13 & = & k_1 + k_2(2)^2 \\
k_ 1 + 4k_2 & = & 13 \ \ldots \unicode{x2461}
\end{array}$
$\unicode{x2461} – \unicode{x2460}$, we have
$\begin{array}{rcl}
3k_2 & = & 6 \\
k_2 & = & 2
\end{array}$
Sub. $k_2=2$ into $\unicode{x2460}$, we have
$\begin{array}{rcl}
k_1 + 2 & = & 7 \\
k_1 & = & 5
\end{array}$
Therefore, $y=5 +2x^2$. If $x=3$, then we have
$\begin{array}{rcl}
y & = & 5 + 2(3)^2 \\
y & = & 23
\end{array}$
