直角坐标系下曲线曲率的计算公式 k=|y''|/(1+y'^2)^(3/2) （*）曲线的方程为 x=r(t)cost,y=r(t)sinty'=dy/dx=(r'sint+rcost)/(r'cost-rsint)y''=dy'/dx=……=(r^2+2r'^2-rr'')/(r'cost-rsint)^2.代入（*）即可....