Question Number 30409 by abdo imad last updated on 22/Feb/18
$${find}\:{lim}_{{n}\rightarrow\infty} \:\:\sum_{\mathrm{1}\leqslant{i}<{j}\leqslant{n}} \:\:{x}^{{i}+{j}} \:\:.{with}\:\mid{x}\mid<\mathrm{1}\:\:. \\ $$
find-lim-n-1-i-lt-j-n-x-i-j-with-x-lt-1-