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?
Lv 5
? asked in Science & MathematicsMathematics · 6 years ago

Verify that the Divergence Theorem is true for the vector field F on the region E.?

Update:

F = <x^2, -y, z>

E is the solid cylinder y^2 + z^2 < 9, 0<x<2

Update 2:

F = <x^2, -y, z>

E is the solid cylinder y^2 + z^2 < 9, 0<x<2

1 Answer

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  • ?
    Lv 7
    6 years ago
    Favorite Answer

    ∫∫ F⋅ dS = ∫∫∫ div F dV

    div F = x

    ∫∫∫ x dx dy dz

    convert to cylindrical

    y = r cos t

    z = r sin t

    x = x

    dx dy dz = r dx dr dt

    ∫[0,2pi] ∫[0,3]∫[0,2] xr dx dr dt

    1/2 (2^2)(1/2)(3^2)(2pi)

    18 pi

    ∫∫ F⋅ dS

    this has to be done in three pieces. The wall of the cylinder, and the top and bottom.

    The bottom

    x = 0

    ∫∫ <0,-y,z><-1,0,0> dy dz

    ∫∫ 0 dy dz

    0

    top cap.

    ∫∫ <2,-y,z><1,0,0> dy dz

    ∫∫ 2 dy dz

    18 pi

    about the wall

    y = 3 cos t

    z = 3 sin t

    x = x

    dS = <dx/dt,dy/dt,dz/dt>x<dx/dx,dy/dx,dz/dx>

    <0, -3 sin t, 3 cos t>X<1,0,0>

    <0,3sin t, 3 cos t>

    ∫ <x^2, -3 cos t, 3 sin t>⋅<0,3sin t, 3 cos t> dx dt

    ∫ 0 dx dt

    0

    18pi = 18 pi

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