即
f(x)=(2x-x^2)^(2/3)
所以
f '(x)=2/3 *(2x-x^2)^(2/3 -1) *(2x-x^2)'
=2/3 *(2x-x^2)^(-1/3) *(2-2x)
=(4-4x)/ 3*(2x-x^2)^1/3