分类常数
y=3x²-3x+2/x²-x+1
=[(3x²-3x+3)-1]/(x²-x+1)
=3-1/(x²-x+1)
∵ x²-x+1=(x-1/2)²+3/4≥3/4
∴ 1/(x²-x+1)∈(0.4/3]
∴ -1/(x²-x+1)∈[-4/3,0)
∴ 3-1/(x²-x+1)∈[5/3,3)
即y=3x²-3x+2/x²-x+1的值域[5/3,3)