球面x^2+y^2+z^2=9,求曲面积分∫(闭合)x^2ds

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球面x^2+y^2+z^2=9,求曲面积分∫(闭合)x^2ds

球面x^2+y^2+z^2=9,求曲面积分∫(闭合)x^2ds
球面x^2+y^2+z^2=9,求曲面积分∫(闭合)x^2ds

球面x^2+y^2+z^2=9,求曲面积分∫(闭合)x^2ds
球面x^2+y^2+z^2=9
∫(闭合)x^2ds=(1/3)∮3x^2ds 因为积分曲面为球面,
根据对称性有,∮x^2ds= ∮y^2ds = ∮z^2ds
=(1/3)∮(x^2+y^2+z^2)ds 因为是曲面积分,所以x^2+y^2+z^2=9可以代入
=(9/3)∮ds=3×4π×3^2=108π

Example 2 in
http://tutorial.math.lamar.edu/Classes/CalcIII/SurfaceIntegrals.aspx
向量r(p,t)=3sinp cost(向量i)+3sinp sint(向量j)+3cosp (向量k)
(1/2)∫(闭合)x^2ds=∫(0,π/2)dp∫(0,2π)dt{ (3sinp cost)^2* ...

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Example 2 in
http://tutorial.math.lamar.edu/Classes/CalcIII/SurfaceIntegrals.aspx
向量r(p,t)=3sinp cost(向量i)+3sinp sint(向量j)+3cosp (向量k)
(1/2)∫(闭合)x^2ds=∫(0,π/2)dp∫(0,2π)dt{ (3sinp cost)^2* 9*sinp
=81∫(0,π/2) (sinp)^3dp∫(0,2π) (cost)^2dt
=81∫(1,0) [-(1-(cosp)^2) d(cosp)]∫(0,2π) (1/2)(1+cos2t)dt
=81(4/3-4)*π
∫(闭合)x^2ds=162*(4/3-4)*π

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