设x=rcos(t),y=rsin(t),r>0,0z}
= PI*S_{z:0->1} ln(1+z^2) dz
= PI*{[zln(1+z^2)]_{z:0->1} - S_{z:0->1}2z^2dz/(1+z^2) }
= PI*[ ln(2) -S_{z:0->1} 2dz + 2S_{z:0->1}dz/(1+z^2) ]
= PI*ln(2) + PI*[ -2z + 2arctan(z) ]_{z:0->1}
= PI*ln(2) + 2PI*[arctan(1) - 1]
= PI[ ln(2) + PI/2 - 2 ]