Asosiy tarkibga o'tish

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.

A three dimensional sketch of the region \(E\) drawn with the traditional axes.  It is the upper half of the sphere of radius 4, a dome sitting on the xy-plane.
A three dimensional sketch of the same upper half of the sphere of radius 4, this time drawn with a set of “box” axes to make the surface and region easier to visualize.

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.