Решите уравнение 5/7 * (21/20-x) + 16/21:8/7=1 1/4

5/7 * (21/20 - х) + 16/21 : 8/7 = 1 1/4

5/7 * (21/20 - х) + 16/21 * 7/8 = 5/4

5/7 * (21/20 - х) + 112/168 = 5/4

5/7 * (21/20 - х) + 14/21 = 5/4

5/7 * (21/20 - х) + 2/3 = 5/4

5/7 * (21/20 - х) = 5/4 - 2/3

5/7 * (21/20 - х) = 15/12 - 8/12

5/7 * (21/20 - х) = 7/12

21/20 - х = 7/12 : 5/7

21/20 - х = 7/12 * 7/5

21/20 - х = 49/60

- х = 49/60 - 21/20

- х = 49/60 - 63/60

- х = - 14/60

х = 14/60

х = 7/30

проверка:

5/7 * (21/20 - 7/30) + 16/21 : 8/7 = 1 1/4

5/7 * (63/60 - 14/60) + 16/21 * 7/8 = 1 1/4

5/7 * 49/60 + 112/168 = 1 1/4

245/420 + 14/21 = 1 1/4

49/84 + 56/84 = 1 1/4

105/84 = 1 1/4

1 21/84 = 1 1/4

1 1/4 = 1 1/4