次のグラフが連続かどうかを調べよ.
(1)f(x,y)=sin(xy)/√(x^2+y^2) ((x,y)≠(0,0)) f(x,y)=0 ((x,y)=(0,0))
(2)f(x,y)=xy^3/(x^2+y^4) ((x,y)≠(0,0)) f(x,y)=0 ((x,y)=(0,0))
(3)f(x,y)=x^2y^2/(x^2+y^4) ((x,y)≠(0,0)) f(x,y)=0 ((x,y)=(0,0))