f(x) = (2x-5)*x^(2/3) = 2x^(5/3) -5x^(2/3)f ′(x) = (10/3)x^(2/3)-(10/3)x^(-1/3)= (10/3)x^(-1/3) * (x-1)单调减区间：（-∞，1)单调增区间：（1，+∞）当x=1时，极小值f(1)=(2-5)*1^(2/3) = -3
