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) lim _((x,y)arrow (0,0))dfrac (1+{x)^2+(y)^2}({x)^2+(y)^2};-|||-(3) lim _((x,y)arrow (0,0))dfrac ({x)^2+(y)^2}(sqrt {1+{x)^2+(y)^2}-1}-|||-(4) lim _((x.y)arrow (0,0))dfrac (xy+1)({x)^4+(y)^4}-|||-(5) lim _((x,y)arrow (1,2))dfrac (1)(2x-y);-|||-(6) lim _((x,y))(0,0)(x+y)sin dfrac (1)({x)^2+(y)^2};-|||-(7) lim _((x,y))(dfrac (sin ({x)^2+(y)^2)}({x)^2+(y)^2}

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

1.试求下列极限(包括非正常极限):-|||-(1) lim _((x,y))(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

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

极限 lim_((x,y)to (0,0)) (x^2 y)/(x^4 + y^2) = ( )A. 等于 0；B. 不存在；C. 等于 $\frac{1}{2

极限 lim_((x,y)to (0,0)) (x^2y)/(x^4 + y^2) ().A. 等于0B. 不存在C. 等于2D. 存在但不等于0

试应用 -8 定义证明:-|||-lim _(x,y))(0,0)dfrac ({x)^2y}({x)^2+(y)^2}=0.

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

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