Ответ:

Пошаговое объяснение:

1)

1/7а+2/7а = 3/7а= 3/7 * 7= 3

3/4n + 5/6n = 9/12n + 10/12n= 19/12n= 19/12 * 6/19= 6/12= 1/2

7/8а - 3/4а= 7/8а- 6/8а = 1/8а= 1/8 * 2 2/3= 1/8* 8/3= 1/3

2)

2/3х+5/6х= 4/6х + 5/6 х= 9/6х= 3/2х= 3/2 * 4= 12/2= 6

5/6m -2/3m = 5/6m - 4/6m = 1/6m = 1/6 * 12= 12/6 = 2

1 5/8х - 3/4х= 13/8х - 6/8х= 7/8х= 7/8 * 4/21= 1/6