Determine the set of points at which the function is continuous
1) G(x,y)=tan^-1((x+y)^-2)
2) f(x,y,z)=√y÷(x^2-y^2+z^2)
3) f(x,y,z)=√z+y+z
4) f(x,y)={x^2y^3÷(2x^2+y^2 if (x,y)≠(0,0)
1 if (x,y)=(0,0)
5) f(x,y)={ xy÷(x^2+xy+y^2 if (x,y)≠(0,0)
0 if (x,y)=(0,0)