下列哪个函数的定义域是有界集？ A: $f(x,y)=e^{-x^2-y^2}$ B: $f(x,y,z)=\sqrt{1-x^2-y^2-z^2}$ C: $f(x,y)=\ln(y-x)$ D: $f(x,y)=\sqrt{1-x^2}+\sqrt{y^2-1}$

‎设置选项让曲面透明和无边界框去观察马鞍面(双曲抛物面)‏ A: Plot3D[x^2-y^2,{x,-3,3},{y,-3,3},PlotStyle→Opacity[0.2],BoxRatios→{1,1,1}] B: Plot3D[x^2-y^2,{x,-3,3},{y,-3,3},BoxRatios→{1,1,1},PlotStyle→Opacity[0.3]] C: Plot3D[x^2-y^2,{x,-3,3},{y,-3,3},PlotStyle→Opacity[1.0],BoxRatios→{1,1,1}] D: Plot3D[x^2-y^2,{x,-3,3},{y,-3,3},BoxRatios→{1,1,1},PlotStyle→Opacity[0.25]]

设置选项让曲面透明和无边界框去观察马鞍面(双曲抛物面) A: Plot3D[x^2-y^2,{x,-3,3},{y,-3,3},PlotStyle→Opacity[0.2], Boxed→False] B: Plot3D[x^2-y^2,{x,-3,3},{y,-3,3},Boxed→False,PlotStyle→Opacity[0.3]] C: Plot3D[x^2-y^2,{x,-3,3},{y,-3,3},PlotStyle→Opacity[1.0],BoxRatios→{1,1,1}] D: Plot3D[x^2-y^2,{x,-3,3},{y,-3,3},BoxRatios→{1,1,1},PlotStyle→Opacity[0.25]]

计算由y=x^2与x^2=2-y所围成的图形面积

二元函数f(x,y)=4x-4y-x^2-y^2的驻点是

\({\lim_{x\to0}}\)\({\lim_{y\to0}}\)xy\(\frac{x^2-y^2}{x^2+y^2}\)= <br/>______

已知x=2008,y=2006,求x-x÷{x^2-y^2/x^3+y^3&#91;(x-x^2+y^2/y)÷(1/x-1/y)&#93;}的值

lim(2x+y)/(x^2-y^2)当x趋近于1,y趋近于2的极限

由双曲线x^2/a^2-y^2/b^2=1,直线y=b,y=-b围成的图形绕y轴旋转一周所得旋转体的体积为

函数f(x，y)=4(x－y)－x^2－y^2（1）有极大值还是极小值（2）极值为