原式=(1/2)a²b-[(3/2)a²b-2(3abc-a²c)-4a²c]-3abc
=(1/2)a²b-[(3/2)a²b-6abc+2a²c-4a²c]-3abc
=(1/2)a²b-(3/2)a²b+6abc-2a²c+4a²c-3abc
=[(1/2)a²b-(3/2)a²b]+(6abc-3abc)+(-2a²c+4a²c)
=-a²b+3abc+2a²c
当a=-1,b=-3,c=1/2时
原式=-(-1)²×(-3)+3×(-1)×(-3)×1/2+2×(-1)²×1/2
=-1×(-3)+3×(-1)×(-3)×1/2+2×1×1/2
=3+(9/2)+1
=(6/2)+(9/2)+(2/2)
=(6+9+2)/2
=17/2 也等于8又2分之1