3、设 (x,y)=arctan dfrac (x)(y), 则 (1,1)=-|||-(A)1; (B)0; (C) dfrac {1)(2),dfrac (1)(2)} : (D) dfrac {1)(2)

7.设 =arctan dfrac (1)(x) ,则 dfrac ({d)^2y}(d{x)^2}(x)_(x=1)= __

2.设D |x|+|y|leqslant 1, 则 iint (|x|+y)dxdy= () .-|||-(A)0 (B) dfrac (1)(3) (C) d

(5)设 (x,y)=ln (x+dfrac (y)(2x)) ,则 _(y)(1,0)= () .-|||-(A)1 (B) dfrac (1)(2) (C)

设(X,Y)的分布函数为(x,y)=dfrac (1)({pi )^2}(dfrac (pi )(2)+arctan dfrac (x)(2))(dfrac (

(B) dfrac (x)(y)((y+1))^2-|||-(C) ^2((x+dfrac {1)(x))}^2. (D) dfrac (y)(x)((y+1)

设L为椭圆dfrac ({x)^2}(2)+dfrac ({y)^2}(3)=1，其周长为a，则dfrac ({x)^2}(2)+dfrac ({y)^2}(3

直线dfrac (x-1)(1)=dfrac (y)(2)=dfrac (z+3)(-2)-|||-__ __-|||-__与平面dfrac (x-1)(1)=

设l为椭圆dfrac ({x)^2}(4)+dfrac ({y)^2}(3)=1，其周长记为a，则dfrac ({x)^2}(4)+dfrac ({y)^2}(

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

[1.3]设(X,Y)的分布律为-|||-Y 1 2 3-|||-X-|||--1 dfrac (1)(3) dfrac (a)(6) dfrac (1)(4)