2Uk=1/(4k+1) -1/(4k+3)=int(0..1)[x^(4k)-x^(4k+2)]dx=int(0..1)[1-x^2]x^(4k)dx
==> 2(somme k=0..n)Uk=int(0..1)[1-x^2](somme k=0..n)x^(4k)dx
Mais (somme k=0..n)x^(4k)=(1-x^(4n+4))/(1-x^4)
(somme de la suite géométrique de raison x^4 pour x#1)
2(somme k=0..n)Uk
=int(0..1)(1-x^(4n+4))/(1+x^2) dx
=int(0..1)1/(1+x^2) dx-int(0..1)x^(4n+4))/(1+x^2) dx
Mais 0<int(0..1)x^(4n+4))/(1+x^2) dx=<int(0..1)x^(4n+4)) dx=1/(4n+5) --->0
==> 2(somme k=0..+oo)Uk =int(0..1)1/(1+x^2) dx=arctan(1)=pi/4
==> (somme k=0..+oo)Uk =pi/8
_________________
وقل ربي زد ني علما