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}(3)=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

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

下列选项中曲面dfrac ({x)^2}(4)+dfrac ({y)^2}(1)+dfrac ({z)^2}(9)=3上点dfrac ({x)^2}(4)+df

求椭球面dfrac ({x)^2}(2)+dfrac ({y)^2}(3)+dfrac ({z)^2}(4)=1上点dfrac ({x)^2}(2)+dfrac

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

[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)

[题目]-|||-椭圆 dfrac ({x)^2}(3)+dfrac ({y)^2}(4)=1 的离心率是 __

((y+dfrac {1)(2))}^2=dfrac (3)(4) D. ((y-dfrac {1)(2))}^2=dfrac (3)(4)

3.设 approx N(0,(4)^2), approx N(1,(3)^2), 且 (rho )_(x)=-dfrac (1)(2), 令 =dfrac (

直线dfrac (x-1)(2)=dfrac (y)(-1)=dfrac (z-2)(3)-|||-__与直线dfrac (x-1)(2)=dfrac (y)(