7.试求下列极限:-|||-(1) lim _((x,y)arrow +infty )dfrac ({x)^2+(y)^2}({x)^4+(y)^4}-|||-(2) lim _((x,y)-(+infty ))((x)^2+(y)^2)(e)^-(x+y);-|||-(3)-|||-(4) lim _((x,y)arrow (+infty ,0))((1+dfrac {1)(x))}^dfrac ({x^2)(x+y)}

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

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

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 1) (x-y)/(x^2)-y^(2)=A. 0 ;B. $\frac{1}{2}$ ;C. $\infty$ ;D. 不存在.

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

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

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