1/2x²-x+1=1/2(x²-2x+1)+1/2=1/2(x-1)²+1/2
当x=3时1/2x²-x+1=1/2(x-1)²+1/2=1/2(3-1)²+1/2=2又1/2
当x=-2时1/2x²-x+1=1/2(x-1)²+1/2=1/2(-2-1)²+1/2=10/2=5
当x=7/2时1/2x²-x+1=1/2(x-1)²+1/2=1/2(7/2-1)²+1/2=25/8+1/2=29/8=3又5/8