f[x_,y_]:=8 Sin[ 2x y]+ (x^2)*y^2-2.5;

(* Find the zero contours of thisfunction *)

Plot3D[f[x,y],{x,-2,2},{y,-2,2},Mesh->False,ViewPoint->{0,0,3}]

(*solution: *)
ContourPlot[f[x,y]==0,{x,-2,2},{y,-2,2}]