Use Stokes' Theorem to evaluate S curl F · dS. F(x, y, z) = x2z2i + y2z2j + xyzk, S is the part of the paraboloid z = x2 + y2 that lies inside the cylinder x2 + y2 = 16, oriented upward.

Respuesta :

Space

Answer:

[tex]\displaystyle \iint_S {\text{curl \bold{F}} \cdot} \, dS = \boxed{\bold{0}}[/tex]

General Formulas and Concepts:

Calculus

Integration Rule [Reverse Power Rule]:

[tex]\displaystyle \int {x^n} \, dx = \frac{x^{n + 1}}{n + 1} + C[/tex]

Integration Rule [Fundamental Theorem of Calculus 1]:

[tex]\displaystyle \int\limits^b_a {f(x)} \, dx = F(b) - F(a)[/tex]

Integration Property [Multiplied Constant]:

[tex]\displaystyle \int {cf(x)} \, dx = c \int {f(x)} \, dx[/tex]

Integration Property [Addition/Subtraction]:

[tex]\displaystyle \int {[f(x) \pm g(x)]} \, dx = \int {f(x)} \, dx \pm \int {g(x)} \, dx[/tex]

Integration Methods: U-Substitution + U-Solve

Multivariable Calculus

Partial Derivatives

Triple Integrals

Cylindrical Coordinate Conversions:

  • [tex]\displaystyle x = r \cos \theta[/tex]
  • [tex]\displaystyle y = r \sin \theta[/tex]
  • [tex]\displaystyle z = z[/tex]
  • [tex]\displaystyle r^2 = x^2 + y^2[/tex]
  • [tex]\displaystyle \tan \theta = \frac{y}{x}[/tex]

Integral Conversion [Cylindrical Coordinates]:

[tex]\displaystyle \iiint_T {f(r, \theta, z)} \, dV = \iiint_T {f(r, \theta, z)r} \, dz \, dr \, d\theta[/tex]

Vector Calculus

Surface Area Differential:

[tex]\displaystyle dS = \textbf{n} \cdot d\sigma[/tex]

Del (Operator):

[tex]\displaystyle \nabla = \hat{\i} \frac{\partial}{\partial x} + \hat{\j} \frac{\partial}{\partial y} + \hat{\text{k}} \frac{\partial}{\partial z}[/tex]

  • [tex]\displaystyle \text{div \bf{F}} = \nabla \cdot \textbf{F}[/tex]
  • [tex]\displaystyle \text{curl \bf{F}} = \nabla \times \textbf{F}[/tex]

Stokes’ Theorem:

[tex]\displaystyle \oint_C {\textbf{F} \cdot } \, d\textbf{r} = \iint_S {\big( \nabla \times \textbf{F} \big) \cdot \textbf{n}} \, d\sigma[/tex]

Divergence Theorem:

[tex]\displaystyle \iint_S {\big( \nabla \times \textbf{F} \big) \cdot \textbf{n}} \, d\sigma = \iiint_D {\nabla \cdot \textbf{F}} \, dV[/tex]

Step-by-step explanation:

Step 1: Define

Identify given.

[tex]\displaystyle \textbf{F} (x, y, z) = x^2z^2 \hat{\i} + y^2z^2 \hat{\j} + xyz \hat{\text{k}}[/tex]

[tex]\displaystyle \text{Region:} \left \{ {{\text{Paraboloid:} \ z = x^2 + y^2} \atop {\text{Cylinder:} \ x^2 + y^2 = 16}} \right[/tex]

Step 2: Integrate Pt. 1

  1. Find div F:
    [tex]\displaystyle \text{div } \textbf{F} = \frac{\partial}{\partial x} x^2z^2 + \frac{\partial}{\partial y} y^2z^2 + \frac{\partial}{\partial z} xyz[/tex]
  2. [div F] Differentiate [Partial Derivatives]:
    [tex]\displaystyle \text{div } \textbf{F} = 2xz^2 + 2yz^2 + xy[/tex]
  3. [Divergence Theorem] Substitute in div F:
    [tex]\displaystyle \iint_S {\text{curl } \textbf{F} \cdot} \, dS = \iiint_D {2xz^2 + 2yz^2 + xy} \, dV[/tex]

Step 3: Integrate Pt. 2

Convert region from rectangular coordinates to cylindrical coordinates.

[tex]\displaystyle \text{Region:} \left \{ {{\text{Paraboloid:} \ z = x^2 + y^2} \atop {\text{Cylinder:} \ x^2 + y^2 = 16}} \right \rightarrow \left \{ {{\text{Paraboloid:} \ z = r^2} \atop {\text{Cylinder:} \ r^2 = 16}} \right[/tex]

Identifying limits, we have the bounds:

[tex]\displaystyle \left\{ \begin{array}{ccc} 0 \leq z \leq r^2 \\ 0 \leq r \leq 4 \\ 0 \leq \theta \leq 2 \pi \end{array}[/tex]

Step 4: Integrate Pt. 3

  1. [Integral] Substitute in variables and region:
    [tex]\displaystyle \iint_S {\text{curl } \textbf{F} \cdot} \, dS = \int\limits^{2 \pi}_0 \int\limits^4_0 \int\limits^{r^2}_0 {r \bigg( 2z^2r \cos \theta + 2z^2r \sin \theta +r^2 \cos \theta \sin \theta \bigg)} \, dz \, dr \, d\theta[/tex]

We evaluate the Stokes' Divergence Theorem Integral using basic integration techniques listed under "Calculus".

[tex]\displaystyle \begin{aligned}\iint_S {\text{curl } \textbf{F} \cdot} \, dS & = \int\limits^{2 \pi}_0 \int\limits^4_0 \int\limits^{r^2}_0 {r \bigg( 2z^2r \cos \theta + 2z^2r \sin \theta +r^2 \cos \theta \sin \theta \bigg)} \, dz \, dr \, d\theta \\& = \frac{1}{3} \int\limits^{2 \pi}_0 \int\limits^4_0 {zr^2 \bigg[ 2z^2 \big( \cos \theta + \sin \theta \big) + 3r \sin \theta \cos \theta \bigg] \bigg| \limits^{z = r^2}_{z = 0}} \, dr \, d\theta \\\end{aligned}[/tex]

[tex]\displaystyle \begin{aligned}\iint_S {\text{curl } \textbf{F} \cdot} \, dS & = \frac{1}{3} \int\limits^{2 \pi}_0 \int\limits^4_0 {r^5 \bigg[ 2r^3 \big( \cos \theta + \sin \theta \big) + 3 \sin \theta \cos \theta \bigg]} \, dr \, d\theta \\& = \frac{1}{54} \int\limits^{2 \pi}_0 {r^6 \bigg[ 4r^3 \big( \cos \theta + \sin \theta \big) + 9 \sin \theta \cos \theta \bigg] \bigg| \limits^{r = 4}_{r = 0}} \, d\theta \\\end{aligned}[/tex]

[tex]\displaystyle \begin{aligned}\iint_S {\text{curl } \textbf{F} \cdot} \, dS & = \frac{2048}{27} \int\limits^{2 \pi}_0 {\cos \theta \Big( 9 \sin \theta + 256 \Big) + 256 \sin \theta} \, d\theta \\& = \frac{-1024}{243} \bigg[ 4608 \cos \theta - \bigg( 9 \sin \theta + 256 \bigg)^2 \bigg] \bigg| \limits^{\theta = 2 \pi}_{\theta = 0} \\& = \boxed{\bold{0}}\end{aligned}[/tex]

∴ we have calculated the Stokes' Theorem integral with the given region and function using the Divergence Theorem.

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Topic: Multivariable Calculus