(2/а(а+б) + 2/б(а+б)) = (2(а+б) + 2(а)) / (а(а+б) * б(а+б)) = (4a + 2b) / ab(a + b)
(х/(х+у) + у/(х-у)) = (x(x - u) + y(x + y)) / (x + y)(x - y) = (x^2 - xu + xy + y^2) / (x^2 - y^2)
(2/а(а+б) + 2/б(а+б)) = (2(а+б) + 2(а)) / (а(а+б) * б(а+б)) = (4a + 2b) / ab(a + b)
(х/(х+у) + у/(х-у)) = (x(x - u) + y(x + y)) / (x + y)(x - y) = (x^2 - xu + xy + y^2) / (x^2 - y^2)