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Q16E
Expert-verifiedTo sketch the solid whose volume is given by the iterated integral and evaluate it.
The value of the given iterated integral is \(\frac{{16\pi }}{3}\).
The region \(D\) is \(\left\{ {(r,\theta ,z)\mid 0 \le r \le 2,0 \le \theta \le 2\pi ,0 \le z \le r} \right\}\).
Integration \(\mathop \smallint \nolimits^b f(x)dx = f(b) - f(a)\)
Since \(r\) varies between \(0\)and \(2\) and \(\theta \) varies between \(0\) and \(2\pi \), the region is the circle in the \(xy\)-plane with radius \(2\) . \(z\)varies from 0 to \(r\). So, the outline sketch of the given region \(D\) is given below in the Figure 1.
Integrate the given iterated integral with respect to \(z\) and apply the limit of it. \(\begin{array}{c}\int_0^2 {\int_0^{2\pi } {\int_0^r r } } dzd\theta dr &=& \int_0^2 {\int_0^{2\pi } {(rz)} _0^rd\theta } dr\\ &=& \int_0^2 {\int_0^{2\pi } {(r(r) - r(0))} _0^rd\theta } dr\\ &=& \int_0^2 {\int_0^{2\pi } {\left( {{r^2} - 0} \right)} } d\theta dr\\ &=& \int_0^{2\pi } {\int_0^{{r^2}} d } \theta dr\end{array}\)
Integrate the given iterated integral with respect to \(r\) and apply the limit of it.
\(\begin{array}{c}\int_0^2 {\int_0^{2\pi } {\int_0^r r } } dzd\theta dr &=& \int_0^2 {\left( {{r^2}\theta } \right)_0^{2\pi }} dr\\ &=& \int_0^2 {\left( {{r^2}(2\pi ) - {r^2}(0)} \right)} dr\\ &=& \int_0^2 {\left( {2\pi {r^2} - 0} \right)} dr\\ &=& \int_0^2 2 \pi {r^2}dr\end{array}\)
Integrate the given iterated integral with respect to \(\theta \) and apply the limit of it.
\(\begin{array}{c}\int_0^2 {\int_0^{2\pi } {\int_0^r r } } dzd\theta dr &=& \left( {2\pi \frac{{{r^3}}}{3}} \right)_0^2\\ &=& 2\pi \left( {\frac{{{2^3}}}{3} - \frac{{{0^3}}}{3}} \right)\\ &=& 2\pi \left( {\frac{8}{3} - 0} \right)\\ &=& \frac{{16\pi }}{3}\end{array}\)
Thus, the value of the given iterated integral is \(\frac{{16\pi }}{3}\).
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