抛物面=dfrac (1)(2)((x)^2+(y)^2) 被平面 =dfrac (1)(2)((x)^2+(y)^2)所截下有限部分的面积是=dfrac (1)(2)((x)^2+(y)^2)( A ) =dfrac (1)(2)((x)^2+(y)^2)( B ) =dfrac (1)(2)((x)^2+(y)^2)( C ) =dfrac (1)(2)((x)^2+(y)^2)( D ) =dfrac (1)(2)((x)^2+(y)^2)

旋转抛物面=dfrac ({x)^2+(y)^2}(2)在=dfrac ({x)^2+(y)^2}(2)那部分的曲面面积S=( )旋转抛物面在那部分的曲面

dfrac (dy)(dx)=(x)^2+(y)^2 B . dfrac (dy)(dx)=(x)^2+(y)^2 C .dfrac (dy)(dx)=(x)^

证明:函数-|||-f(x,y)= ((x)^2+(y)^2)sin dfrac (1)(sqrt {{x)^2+(y)^2}}, ^2+(y)^2neq 0,

设函数 (x,y)=1-dfrac (cos sqrt {{x)^2+(y)^2}}(tan ({x)^2+(y)^2)} ,则当定设函数 (x,y)=1-df

5.求密度分布均匀的抛物面 =dfrac (1)(2)((x)^2+(y)^2)(zleqslant 2) 的质心.

7.设 (x,y)=dfrac (1)(xy),r=sqrt ({x)^2+(y)^2} _(1)= (x,y)|(x,y)in {R)^2 dfrac (1)

设 (x,y)=dfrac ({x)^2+(y)^2}({e)^xy+xysqrt ({x)^2+(y)^2}} ,则 (f)_(x)(1,0)= __ _.

1.设 (x,y,z)=dfrac (z)({x)^2+(y)^2}, 则 df(1,2,1)= __

6.讨论下列函数的连续性:-|||-(1) (x,y)=dfrac ({x)^2-(y)^2}({x)^2+(y)^2}-|||-(2) (x,y)=dfrac

6.设 (x,y)=dfrac (x-{y)^2+(y)^3}(2x+{y)^2}, 则,lim h(x,y)等于 ()-|||-(A) dfrac (1)(2