Darstellung einer Ellipse mittels impliziter Gleichung

<< Graphics`ImplicitPlot`

f[x, y] := x^2/25 + y^2/(3.5)^2 - 1
ImplicitPlot[f[x, y] == 0, {x, -6, 6}, {y, -4, 4},  
      AspectRatio -> Automatic,  AxesOrigin -> {0, 0}, 
      AxesLabel -> {"x", "y"}]