(1 - 2х) : (х + 13) = - 3 : 1

(1 - 2х) * 1 = (х + 13) * (-3)        свойство пропорции

1 - 2х = -3х - 39

-2х + 3х = -39 - 1

х = - 40

Проверка: (1 - 2 * (-40)) : ((-40) + 13) = - 3

                   (1 + 80) : (-27) = - 3

                    81 : (-27) = - 3 - верно.      

Verified answer