решить уравнение
И заранее

(12 5/13 +у ) - 9 9/13= 7/13
( 12 5/13+у) = 7/13+ 9 9/13
12 5/13 +у = 9 16/13= 10 3/13
У= 10 3/13 - 12 5/13
10 3/13 - 12 5/13= - (12 5/13-10 3/13)= - 2 2/13
У= - 2 2/13
Проверка:
12 5/13 - 2 2/13 - 9 9/13= 1 (3-9)/13= (16-9)/13= 7/13
7/13=7/13

(Х - 3 13/21 ) + 2 10/21 = 7 2/21
(Х- 3 13/21) = 7 2/21 - 2 10/21
Х - 3 13/21 = 6 23/21 - 2 10/21
X-3 13/21= 4 13/21
X= 4 13/21 + 3 13/21
X= 7 26/21=8 5/21
X= 8 5/21
Проверка:
8 5/21 - 3 13/21 + 2 10/21 = 7 26/21 - 3 13/21 +2 10/21 = 6 23/21= 7 2/21
7 2/21 = 7 2/21