Processing math: 100%
f(x,y)=y2x24
f(x,y)=sinx2+y2
f(x,y)={x3yxy3x2+y2,(x,y)(0,0);0,(x,y)=(0,0).
f(x,y)=ey/4cos(2x)
f(x,y)=cos(2x)cos(2y)
f(x,y)=ln(4(x2+y2))2