lim _(x arrow 1) (x-y)/(x^2)-y^(2)=

4.证明:(1) lim _((x,y)arrow (0,0))dfrac (x+y)(x-y) 不存在;(2)-|||-lim _((x,y)arrow (0

7.试求下列极限:-|||-(1) lim _((x,y)arrow +infty )dfrac ({x)^2+(y)^2}({x)^4+(y)^4}-|||-

试求下列极限(包括非正常极限):-|||-(1) lim _((x,y))(dfrac ({x)^2(y)^2}({x)^2+(y)^2}-|||-(2) li

lim_(x arrow + infty)(x^2+y^2)sin (3)/(x^2)+y^(2)A. 0B. 3C. 1/3D. ∞

1.试求下列极限(包括非正常极限):-|||-(1) lim _((x,y)arrow (0,0))dfrac ({x)^2(y)^2}({x)^2+(y)^2

6.求下列各极限:-|||-(1) lim _((x,y)arrow (0,1))dfrac (1-xy)({x)^2+(y)^2} :-|||-(3) lim

6.求下列各极限:-|||-(1) lim _((x,y)arrow (0,1))dfrac (1-xy)({x)^2+(y)^2} ;-|||-(3) lim

求函数的极限 lim _(x arrow 2) (tan x y)/(y)=A. 0B. 2C. 不存在D. $\infty$

lim _(x arrow 2) (sin xy)/(y) = ( )A. $\infty$B. 0C. 1D. 2

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)