let ∣a∣<1 and f(a)=∫_0 ^1 ln(x)ln(1+ax)dx
1) find a explicit form of f(a)
2) calculate g(a) =∫_0 ^1 ((xln(x))/(1+ax))dx
3) calculate ∫_0 ^1 ln(x)ln(2+x)dx
4) calculate ∫_0 ^1 ((xln(x))/(2+x))dx
5) calculate u_n =∫_0 ^1 ((xln(x))/(n+x))dx with n integr and n>1
find nature of the serie Σ u_n