(1)对函数f(x)求导:
f(x)'=(3ax-ax^2)/e^x
令f(x)'=0 即3ax-ax^2=0
a>0..解得:x=0或3
则在(-无穷,0)与(3,+无穷)单调减
在(0,3)单调增.
(2)|f(x1)-f(x2)|