Х/3 - Х/7= 3 3/7
(Х•7)/(3•7)- (Х•3)/(7•3)=
((3•7+3)•3)/(7•3)
7х/21- 3х/21= 72/21
4х/21= 72/21
Х= 72/21: 4/21
Х= 72/21• 21/4
Сокращаем 21 и 21 на 21; 72 и 4 на 4.
Х= 18/1• 1/1
Х= 18
Проверка
Х/3 - Х/7= 3 3/7
18/3- 18/7= 3 3/7
6- 2 4/7= 3 3/7
5 7/7- 2 4/7=3 3/7
3 3/7= 3 3/7