曲率κ=│y''│/(1+y'²)^(3/2)
曲线y=x^3(x>=0)
曲率κ=6x/(1+9x^4)^(3/2)
κ'=6(1-45x^4)/(1+9x^4)^(5/2)
分析上式可知当x=1/45^(1/4)时,有最大曲率
κ(1/45^(1/4))=(5^1.25)/[3√2]