5.求下列极限:-|||-(1) lim _(xarrow 0)dfrac (1-xy)({x)^2+(y)^2} :-|||-(3) lim _(xarrow 0)dfrac (2-sqrt {xy+4)}(xy)-|||-(5) lim _(xarrow 0)([ 1+sin (xy)] )^dfrac (y{x)} :-|||-(2) lim _(xarrow 0)(x+y)sin dfrac (1)({x)^2+(y)^2} ,-|||-(4) lim _(xarrow 0)[ dfrac (sin (xy))(x)+((x+y))^2] =-|||-(6) lim _(xarrow 0)dfrac (1-{e)^(x^2+{y)^2}}(x+1)dfrac (1-{e)^(x^2+{y)^2}}(ln (1+2{x)^2+2(y)^2)}