Câu $8:$$\\$ $V = \pi \displaystyle\int_{0}^{2} (2^x)^2 dx\\ V = \pi \displaystyle\int_{0}^{2} 4^x dx\\ \Rightarrow\rm D$$\\$ Câu $9:$ $x^2- 2x- 8 = 0\\\left[ \begin{aligned} x = 4 \\ x = -2 \end{aligned} \right.\\ \Rightarrow S = \displaystyle\int_{-2}^{4} |x^2- 2x- 8| dx$$\\$ Do $x^2- 2x- 8 \le 0$ trên đoạn $[-2; 4]$$\\$ $S = \displaystyle\int_{-2}^{4} -(x^2- 2x- 8) dx\\ S = \displaystyle\int_{-2}^{4} (8+ 2x- x^2) dx$$\\$ $\Rightarrow\rm D$