Mathematica算负数的三次方根时取的是虚数，注意：x^(1/3) = Sign[x]*Abs[x]^(1/3)函数x^2+[y-x^(1/3)]=1，即：y=1-x^2+x^(1/3)代码：Plot[1-x^2+Sign[x]*Abs[x]^(1/3), {x, -1, 1 }]
