15.7-bo'lim : Sferik koordinatalarda uch karrali integrallar
1. \( \displaystyle \iiint\limits_{E}{{10xz + 3\,dV}}\) ni baholang, bunda \(E\) \({x^2} + {y^2} + {z^2} = 16\) ning \(z \ge 0\) bilan mintaqaviy qismidir.
Yechim
Mayli, keling, \(E\) hududining qisqacha chizmasidan boshlaylik, shunda biz nima bilan shug'ullanayotganimizni his qilamiz.


Biz "an'anaviy" o'qlar to'plami bilan bir qatorda "quti" o'qlari to'plami bilan eskizlarni berdik, bu sirt va mintaqani tasavvur qilishda yordam beradi.
Bu holda biz 4 radiusli sharning yuqori yarmi bilan ishlaymiz.
2-qadam
Endi, biz sharning bir qismini integrallashayotganimiz sababli, integral uchun sferik koordinatadan foydalanish mantiqiy va chegaralar:
\[\begin{array}{c}0 \le \varphi \le \frac{\pi }{2}\\ 0 \le \theta \le 2\pi \\ 0 \le \rho \le 4\end{array}\]Esda tutingki, \(\varphi \) - bu mintaqani qamrab olganimizda biz aylanayotgan musbat \(z\) o'qidan burchak va \(\theta \) - mintaqani qamrab olganimizda \(z\) o'qi atrofida aylantiradigan burchak.
Bu holda bizda sharning to'liq yuqori yarmi bor va shuning uchun \(\theta \) 0 dan \(2\pi \) gacha, \(\varphi \) esa 0 dan \(\frac{\pi }{2}\) gacha bo'ladi.
3-qadam
ushbu limitlarni integralga ulash va sferik koordinatalarga aylantirish,
\[\begin{align*}\iiint\limits_{E}{{10xz + 3\,dV}}& = \int_{0}^{{\frac{\pi }{2}}}{{\int_{0}^{{2\pi }}{{\int_{0}^{4}{{\left[ {10\left( {\rho \sin \varphi \cos \theta } \right)\left( {\rho \cos \varphi } \right) + 3} \right]\left( {{\rho ^2}\sin \varphi } \right)\,d\rho }}\,d\theta }}\,d\varphi }}\\ & = \int_{0}^{{\frac{\pi }{2}}}{{\int_{0}^{{2\pi }}{{\int_{0}^{4}{{10{\rho ^4}{{\sin }^2}\varphi \cos \varphi \cos \theta + 3{\rho ^2}\sin \varphi \,d\rho }}\,d\theta }}\,d\varphi }}\end{align*}\]\(x\) va \(z\)-ni sferik koordinatalarga aylantirishni unutmang, shuningdek, \(dV = {\rho ^2}\sin \varphi \,d\rho \,d\theta \,d\varphi \)-ni unutmang, shuning uchun biz \(dV\)-ni sferik koordinatalarga o'tkazishda bir nechta qo'shimcha shartlarni tanlaymiz.
4-qadam
OK, endi biz qilishimiz kerak bo'lgan narsa - bu integralni baholash. Mana \(\rho \) integratsiyasi.
\[\begin{align*}\iiint\limits_{E}{{10xz + 3\,dV}} & = \int_{0}^{{\frac{\pi }{2}}}{{\int_{0}^{{2\pi }}{{\left. {\left( {2{\rho ^5}{{\sin }^2}\varphi \cos \varphi \cos \theta + {\rho ^3}\sin \varphi } \right)} \right|_0^4\,d\theta }}\,d\varphi }}\\ & = \int_{0}^{{\frac{\pi }{2}}}{{\int_{0}^{{2\pi }}{{2048{{\sin }^2}\varphi \cos \varphi \cos \theta + 64\sin \varphi \,\,d\theta }}\,d\varphi }}\end{align*}\]5-qadam
Keling, \(\theta \) integratsiyasini amalga oshiramiz.
\[\begin{align*}\iiint\limits_{E}{{10xz + 3\,dV}} & = \int_{0}^{{\frac{\pi }{2}}}{{\left. {\left( {2048{{\sin }^2}\varphi \cos \varphi \sin \theta + 64\theta \sin \varphi } \right)} \right|_0^{2\pi }\,d\varphi }}\\ & = \int_{0}^{{\frac{\pi }{2}}}{{128\pi \sin \varphi \,d\varphi }}\end{align*}\]6-qadam
Va nihoyat, biz \(\varphi \) integratsiyasini amalga oshiramiz.
\[\iiint\limits_{E}{{10xz + 3\,dV}} = \left. {\left( { - 128\pi \cos \varphi } \right)} \right|_0^{\frac{\pi }{2}} = \require{bbox} \bbox[2pt,border:1px solid black]{{128\pi }}\]E'tibor bering, bu holda, har bir integralning chegaralari doimiylar bo'lganligi sababli, biz xohlagan tartibda integratsiyani amalga oshirishimiz mumkin edi. Bunday holda, \(\varphi \) ni birinchi yoki ikkinchi marta bajarish "oddiyroq" bo'lishi mumkin edi, chunki bu qolgan integral(lar) uchun integrani sezilarli darajada kamaytiradi.