()-|||-A (x)=(x)^2-(y)^2+2xy+i((y)^2-(x)^2)-|||-B (x)=(x)^2-(y)^2+2xy+i((y)^2+2xy-(x)^2)-|||-C (x)=(x)^2-(y)^2+2xy+i((y)^2+xy-(x)^2)-|||-D (x)=(x)^2-(y)^2+2xy+i((y)^2-2xy-(x)^2)

(x,y)=(x)^2-(y)^2-x-|||-__ B . (x,y)=(x)^2-(y)^2-x-|||-__C . (x,y)=(x)^2-(y)^2-x

(z)=(x)^2-(y)^2+2xy-|||-__ 是单值函数。是单值函数。A.对B.错

微分方程x^2y`+xy= y^2, y|x=1=1 的特解为A x^2y`+xy= y^2, y|x=1=1 B x^2y`+xy= y^2, y|x=1=1

设=dfrac (2x)({x)^2-(y)^2} ，则 =dfrac (2x)({x)^2-(y)^2}=dfrac (2x)({x)^2-(y)^2}___

函数(x.y)=4x-(x)^2-(y)^2的极值为（ ）(x.y)=4x-(x)^2-(y)^2(x.y)=4x-(x)^2-(y)^2(x.y)=4x-(x

2.已知 dfrac (x)(x+y)=dfrac (1)(3) ,求 dfrac ({x)^2-(y)^2}(2xy+{y)^2} 的值.

证明u(x,y)=(x-y)(x^2+4 xy+y^2)u(x,y)=(x-y)(x^2+4 xy+y^2)u(x,y)=(x-y)(x^2+4 xy+y^2)

已知压和函数=(y)^2-(x)^2, 求解析函数 数=(y)^2-(x)^2 使得数=(y)^2-(x)^2已知压和函,求解析函数使得

以曲线 ) z=(x)^2+2(y)^2 z=2-(x)^2 .B 、 ) z=(x)^2+2(y)^2 z=2-(x)^2 .以曲线在平面上的投影曲线

已知x，y都是正数，且x≠y，求证：（1）(x)/(y)+(y)/(x)＞2；（2）(2xy)/(x+y)＜sqrt(xy)．已知x，y都是正数，且x≠y，求证