Example (ii)

Plot3D[((1-Cos[Sqrt[(x^2)+(y^2)]])/((x^2)+(y^2))),{x,-3,3},{y,-3,3},PlotPoints->50,AxesLabel->{x,y,z}]

Example (iii)

Plot3D[((2x+y)/(x+y)),{x,-3,3},{y,-3,3},PlotPoints->50,AxesLabel->{x,y,z}]

ContourPlot[((2x+y)/(x+y)),{x,-3,3},{y,-3,3}]

Example (iv)

ContourPlot[((x^2)/((x^2)+y)),{x,-3,3},{y,-3,3}]