3x-1/7x+1=2/5

3x-1/7x+1=2/5   5(3x-1)=2(7x+1)   15x -5=14x +2 x=7

3x - 1/7x + 1 = 2/5 7x + 1 ≠ 0    --> 5 ≠ 0 7x ≠ -1/ :7 x = -1/7 D = R - - {1/7} (3x - 1) * 5 = 2 * (7x + 1) 15x - 5 = 14x + 2 15x - 14x = 2 + 5 x = 7 ∈ D