Lean-Workbook Plus 60816: Exponential identity

For real $x$, $(e^x+1)(e^x+x+1)=e^{2x}+(x+2)e^x+x+1$.

Source: Lean-Workbook row lean_workbook_plus_60816 (Apache-2.0). The unchanged proposition comes from the original record; its missing mathematical imports and namespaces are restored here.