y = 1 x , x = 1 , x = 2 , y = 0 ; about the x-axis {\displaystyle y={\frac {1}{x}},x=1,x=2,y=0;{\text{about the x-axis}}}
π / i n t 1 2 {\displaystyle {\begin{aligned}\pi /int_{1}^{2}\end{aligned}}}
