(∫_0^∞)(∫_0^x)2 (E^(-x))(E^(-y))\[DifferentialD]y\[DifferentialD]x

Plot3D[2 (E^(-x))(E^(-y)),{x,0,3},{y,0,x},PlotRange->All]

ContourPlot[2 (E^(-x))(E^(-y)),{x,0,3},{y,0,x},PlotRange->All]

(∫_0^x)2 (E^(-x))(E^(-y))\[DifferentialD]y

Integrate[2 (E^(-2 x)) (-1+(E^x)),{x,0,∞}]

Plot[2 (E^(-2 x)) (-1+(E^x)),{x,0,5}]

(∫_y^∞)2 (E^(-x))(E^(-y))\[DifferentialD]x