y= x ^3(1-x)=x^3-x^4 y'=3x^2-4x^3 y'=0 x=0或3/4 y'>0,单调递减，递减区间为x={x|x>3/4} y'<0,单调递增，递增区间为x={x|x<3/4} 极值点(拐点)有两个x=0和x=3/4 x=0 y=0 x=3/4 y=27/256
