f = Sqrt[x^2 + y^2]+Sqrt[1-x^2]+Sqrt[1-y^2]

gradijent = D[f,{{x,y}}]

Tacke = Solve[gradijent == 0,{x,y}]

Hodf= Simplify[D[f,{{x,y},2}]]

HodfM = MatrixForm[Hodf]

HodfuTacke = Hodf  /. Tacke

minf = Map[PositiveDefiniteMatrixQ,HodfuTacke,1]

maxf = Map[PositiveDefiniteMatrixQ,-HodfuTacke,1]

Plot3D[f,{x,-1,1},{y,-1,1},ColorFunction->Hue,PlotRange->{{-1.1,1.1},{-1.1,1.1},{1,2.5}}]

Show[%27,ImageSize->Full]