:∫∫ln(1 x^2 y^2)dσ,其中D是由圆周x^2 y^2=1及坐
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∫ln(1+x²)dx=x•ln(1+x²)-∫xdln(1+x²)=xln(1+x²)-∫x•1/(1+x²)•
极坐标∫∫(D)ln(1+x²+y²)dxdy=∫∫(D)rln(1+r²)drdθ=∫[0→2π]dθ∫[0→1]rln(1+r²)dr=2π∫[0→1]rl
{x=rcosθ、y=rsinθe²≤x²+y²≤e⁴→e²≤r²≤e⁴→e≤r≤e²∫∫_[D]ln(x²
再问:极径r积分区域为什么是0
答:设极坐标x=cosθ,y=sinθ,1
chainruley=f(g(x))y'=g'(x)f'(g(x))
Y=[LN(1-X)]^2?Y'=2LN|1-X|/(1-X)(-1)=-2LN|1-X|/(1-X)
用分部积分法,(uv)'=u'v+uv',设u=ln(1+x^2),v'=1,u'=2x/(1+x^2),v=x,原式=xln(1+x^2)-2∫x^2dx/(1+x^2)=xln(1+x^2)-2∫
解(极坐标法):做变换,设x=rcosθ,y=rsinθ,则dxdy=rdθdr∴原式=∫(0,2π)dθ∫(a,b)rlnrdr=2π∫(a,b)rlnrdr=2π[(r²lnr/2)|(
d(ln(x^2+y))=[1/(x^2+y)].(2xdx+dy)再问:那d(2y-t*y^2)怎么算再答:t是常数d(2y-t*y^2)=(2-2ty)dyt是变数d(2y-t*y^2)=2dy-
y'=(1+x/√(1+x^2))/(x+√(1+x^2))=1/√(1+x^2)y''=-x/(1+x^2)^(3/2)
∫(r^2/r^2+1)dr=∫dr-∫1/(r^2+1)dr再问:∫1/(r^2+1)dr怎么求再答:arctanr
当中那个式子有问题,应该等于=-∫(ln(x+1)-lnx)d(ln(x+1)-lnx),有个负号再问:恩我主要想知道最后答案是怎么得出来的再答:有个公式:∫f(x)d[f(x)]=[f(x)]^2/
2x/(1+x^2)
y'=ln(2x^-1)'=(x/2)*2*(-1)/x^2=-1/x
x≤0时√x^2=-x所以y=0x>0时√x^2=x所以y=ln(2x+1)