y=(2x²-3x-1)÷(x²)=2-﹙3/x+1/x²﹚=2-﹙9/4-9/4﹢3/x+1/x²﹚=17/4-﹙1/x﹢3/2﹚²
﹙1/x﹢3/2﹚²≧0,所以y=17/4-﹙1/x﹢3/2﹚²≦17/4
所以值域为[﹣∞,17/4﹚