1) 13 - (2х - 5) = х - 9
13 - 2х + 5 = х - 9
- 2х - х = - 9 - 5 - 13
- 3х = - 27
х = - 27 : (-3)
х = 9
Проверка: 13 - (2 · 9 - 5) = 9 - 9
13 - (18 - 5) = 0
13 - 13 = 0
2) 3х - (10 - 9х) = 22
3х - 10 + 9х = 22
3х + 9х = 22 + 10
12х = 32
х = 32 : 12
х = 32/12 = 8/3
х = 2 целых 2/3
Проверка: 3 · 8/3 - (10 - 9 · 8/3) = 22
8 - (10 - 3 · 8) = 22
8 - (10 - 24) = 22
8 - (-14) = 22
8 + 14 = 22
3) 26 - (17 - 2х) = 5х
26 - 17 + 2х = 5х
9 = 5х - 2х
9 = 3х
х = 9 : 3
х = 3
Проверка: 26 - (17 - 2 · 3) = 5 · 3
26 - (17 - 6) = 15
26 - 11 = 15
1000-270=730 грамм маса 1л бензина