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code:

Manipulate[{Plot3D[{{function}}, {x, -3, 3}, {y, -3, 3}, 
   AxesLabel -> {x, y, "f(x,y)"}, MeshFunctions -> {#3 &}, Mesh -> 5],
   ContourPlot[function, {x, -3, 3}, {y, -3, 3}]}, {{function, 
   5 - x^2/2 - y^2, 
   Style["Función=", 14, Purple]}, {5 - x^2/2 - y^2 -> 
    TraditionalForm[5 - x^2/2 - y^2], 
   x^2/2 + y^2 -> TraditionalForm[x^2/2 + y^2], 
   1 - 2 x + y -> TraditionalForm[1 - 2 x + y], 
   x^2/2 - y^2 -> TraditionalForm[x^2/2 - y^2], -x^2/2 + y^2 -> 
    TraditionalForm[-x^2/2 + y^2], 
   Sin[Sin[y] + Sin[x]] -> TraditionalForm[Sin[Sin[y] + Sin[x]]], 
   x y E^(-0.4 (x^2 + y^2)) -> 
    TraditionalForm[x y E^(-0.4 (x^2 + y^2))]}}]