重积分的计算毕业论文

The second surface integral calculation is a difficulty and key content of higher mathematics. The second curved surface integral, also known as sitting target surface integral, it said the physical significance of the steady flow of incompressible fluid flow to the surface side of the flow. The second kind of surface integral calculation problem is a comprehensive calculus problem, involves the surface side and the normal vector, partial derivative of function of many variables, double integral and triple integrals, the first kind of curved surface integral and gauss formula, and other knowledge.This article, we respectively from two traditional calculation method and an innovative method to calculate the direction of generalizations about the second type of surface integral calculation method, and combined with typical examples illustrate the use of different methods, easy to master by the techniques of.

利用极坐标计算二重积分,有公式 ∫∫f(x,y)dxdy=∫∫f(rcosθ,rsinθ)rdrdθ ,其中积分区域是一样的. I=∫dx∫(x^2+y^2)^-1/2 dy x的积分上限是1,下限0 y的积分上限是x,下限是x² 积分区域D即为直线y=x,和直线y=x²在区间[0,1]所围成的面积,转换为极坐标后,θ的范围为[0,π/4],下面计算r的范围： 因为y=x²的极坐标方程为：rsinθ=r²cos²θ r=sinθ/cos²θ 因为直线y=kx和曲线y=x²的交点为(0,0),(k,k²),所以在极坐标中r的取值范围为[0,sinθ/cos²θ],则积分I化为极坐标的积分为 I＝∫dθ∫1/√(rcosθ)²+(rsinθ)²rdr =∫dθ∫dr (θ范围[0,π/4],r范围[0,sinθ/cos²θ]) =∫(sinθ/cos²θ)dθ(θ范围[0,π/4]) =∫(-1/cos²θ)dcosθ =|1/cosθ|(θ范围[0,π/4]) =1/cos(π/4)-1/cos0 =√2-1