f(x)=-(x-3)|x|
f(x)=-(x-3)x (x>=0)
f'(x)=-2x+3>=0
=>0<=x<=3/2
f(x)=(x-3)x (x<0)
f'(x)=2x-3>0
无解.
=>单调增区间:0<=x<=3/2