1/3х + 1/5х + 1/6х = 21/40 (ОДЗ: х не равно 0) 10/30х + 6/30х + 5/30х = 21/40 21/30х=21/40 (поделим ну 21) 1/30х = 1/40 30х = 40 х = 40/30 х = 4/3 х = 1цел 1/3