grandes-ecoles 2022 Q12

grandes-ecoles · France · mines-ponts-maths1__mp Reduction Formulae Connect a Discrete Sum to an Integral via Reduction Formulae
Prove, without using what precedes, that
$$\int _ { 0 } ^ { + \infty } \frac { x e ^ { - x } } { 1 - e ^ { - x } } \mathrm {~d} x = \frac { \pi ^ { 2 } } { 6 }$$
Prove, without using what precedes, that

$$\int _ { 0 } ^ { + \infty } \frac { x e ^ { - x } } { 1 - e ^ { - x } } \mathrm {~d} x = \frac { \pi ^ { 2 } } { 6 }$$