a=b-3
a-b=-3
于是
1/2(a-b)²-3/5(a-b)-3/2(a-b)²-2/5(a-b)-3
=1/2(a-b)²-3/2(a-b)²-[3/5(a-b)+2/5(a-b)]-3
=-(a-b)²-(a-b)-3
=-(-3)²-(-3)-3
=-9+3-3
=-9
a=b-3
a-b=-3
于是
1/2(a-b)²-3/5(a-b)-3/2(a-b)²-2/5(a-b)-3
=1/2(a-b)²-3/2(a-b)²-[3/5(a-b)+2/5(a-b)]-3
=-(a-b)²-(a-b)-3
=-(-3)²-(-3)-3
=-9+3-3
=-9