2. The graphs of the functions $y=2x$ and $y=\frac{18}{x}$ intersect at points $A$ and $B$ (where $A$ is in the first quadrant). A perpendicular line $AC$ is drawn from $A$ to the $x$-axis, with the foot of the perpendicular being $C$. The area of $\triangle ABC$ is equal to ( ).
(A) 6
(B) 9
(C) 12
(D) 18
2.D.

Solve the system of equations $\left\{\begin{array}{l}y=2 x, \\ y=\frac{18}{x}\end{array}\right.$. The solutions are $A(3,6), B(-3,-6)$, so $C(3,0)$. Therefore, $S_{\triangle A B C}=\frac{1}{2} \times 6 \times[3-(-3)]=18$.