SetDirectory["C:\\drorbn\\AcademicPensieve\\Talks\\Matemale-1804"]

MakeImage["RestrictingAQuadratic", Show[
Plot3D[(x^2)+(y^2), {x,-1,1},{y,-1,1}, Boxed -> False, Ticks->False, Axes->False],
ParametricPlot3D[{t-0.5(1-t), -0.5t+(1-t), (((t-0.5(1-t)))^2)+(((-0.5t+(1-t)))^2)}, {t,0,1}, PlotStyle -> {Red, Opacity[1],Thickness[0.05]}],
Graphics3D@{Blue,Opacity[0.5],Polygon@{{1,-0.5,0},{-0.5,1,0},{-0.5,1,2},{1,-0.5,2}}},
AspectRatio -> 1, ViewPoint->{-2.93879,-0.903137,1.41345},ViewVertical->{0.,0.,1.}
], ImageSize->800]