Bài tập 38 trang 175 SGK Toán 12 NC

\(\begin{array}{*{20}{l}}
\begin{array}{l}
V = \pi \int\limits_0^{\frac{\pi }{4}} {{{\cos }^2}xdx} \\
 = \frac{\pi }{2}\int\limits_0^{\frac{\pi }{4}} {\left( {1 + {{\cos }^2}} \right)xdx} 
\end{array}\\
\begin{array}{l}
 = \left. {\frac{\pi }{2}.\left( {x + \frac{1}{2}\sin 2x} \right)} \right|_0^{\frac{\pi }{4}}\\
 = \frac{\pi }{2}\left( {\frac{\pi }{4} + \frac{1}{2}} \right) = \frac{{\pi \left( {\pi  + 2} \right)}}{8}
\end{array}
\end{array}\)

-- Mod Toán 12 HỌC247