就是y＝x^(2/3)了
由立方差公式,△y＝(x+h)^(2/3)－x^(2/3)
＝[(x+h)^2-x^2]/[(x+h)^(4/3)＋(x^2+hx)^(2/3)＋x^(4/3)]
＝h(2x＋h)/[(x+h)^(4/3)＋(x^2+hx)^(2/3)＋x^(4/3)]
所以,△y/h＝(2x＋h)/[(x+h)^(4/3)＋(x^2+hx)^(2/3)＋x^(4/3)],当h→0时,极限是 2x/[x^(4/3)＋x^(4/3)＋x^(4/3)]＝2/3×x^(-1/3)
所以,x^(2/3)的导数是2/3×x^(-1/3)