椭圆 dfrac ({x)^2}(m)+dfrac ({y)^2}(8)=1 的焦距是2,则m的值是 ()-|||-A.9 B.7或10-|||-C.7或9 D.25

(4)已知 =xln x, 则 y(10) 等于 ()-|||-(A) -dfrac (1)({x)^9} (B) dfrac (1)({x)^9} (C) d

dfrac (7)(2) D. dfrac (9)(2)

(10)设 = (x,y)|dfrac {{x)^2}(4)+dfrac ({y)^2}(9)leqslant 1} , 则dxdy等于 () .-|||-A.

9.随机变量X的概率密度为: f(x)= ; (B) dfrac {5)(8) (C) dfrac (7)(8) (D) dfrac (1)(2)

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

dfrac (1)(5)(X)_(1)+dfrac (2)(5)(X)_(2)+dfrac (2)(5)(X)_(3)-|||-D .dfrac (1)(7)(

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 ({

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

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

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