高数之曲率对数曲线y=lnx上哪一点处的曲率半径最小?求出该点处的曲率半径.答案是（根号2/2,-ln2/2)处曲率半径有最小值3根号3/2.

y=lnxy'=1/xy''=-x^(-2)曲率半径公式ρ=[(1+y'^2)^(3/2)]/∣y"∣= (1+ (1/x)^2)^(3/2) / (x^(-2))=x^2 * (1+ x^(-2) )^(3/2)对它求导=2x*(1+x^(-2))^(3/2) +x^2 * 3/2*(1+x^(-2))^(1/2) *(-2)x^(-3)=2x*(1+x^(-2))*(...