14.确定下列函数极限是否存在,若存在则求出极限:-|||-(1) lim _(xarrow (x))(dfrac (x)(x)) 其中 = (x,y):ygt {x)^2} ;-|||-(2) lim _((x,y)arrow (0,0))xln ((x)^2+(y)^2);-|||-(3) lim _((x,y)|arrow +infty )((x)^2+(y)^2)(e)^-(|x|+|y|);-|||-(4) |lim _(xarrow 0)||-dfrac ({x)^2}(|x|+|y|)-|||-(5) lim _((x,y)zxarrow (0,0,0))((dfrac {xyz)({x)^2+(y)^2+(z)^2})}^x+y-|||-(6) Longrightarrow (x,y,z)arrow (0,0,0) (x)^yz, 其中 = (x,y,z):x,y,zgt 0 ;-|||-(7) (x,y,z)arrow (0,1,0)dfrac (sin (xyz))({x)^2+(z)^2};-|||-(8) lim _((x,y,z)arrow (0,0,0))dfrac (sin xyz)(sqrt {{x)^2+(y)^2+(z)^2}}-|||-(9) lim _(xarrow 0)dfrac ({(sum _{i=1)^n(x)_(i))}^2}({|x|)^2}