f'(x)=x^(2/3)+2x/3·x^(-1/3)-2/3·x^(-1/3)=x^(2/3)+2/3·x^(2/3)-2/3·x^(-1/3)=5/3·x^(2/3)-2/3·x^(-1/3)=(5x-2)/3·x^(-1/3)=(5x-2)/(3·³√x)
