Question Number 34290 by math khazana by abdo last updated on 03/May/18
$${calculate}\:\int\int_{{D}} \:\:\:\:\:\:\:\frac{{dxdy}}{\left(\mathrm{1}+{x}+{y}\right)^{\mathrm{2}} } \\ $$$${D}\:=\left\{\left({x},{y}\right)\in\:{R}^{\mathrm{2}} \:/\:\:\mathrm{1}\leqslant{x}+{y}\leqslant\:\mathrm{2}\right\}\: \\ $$