2(у+3)=21-3у; (2- с)+3(с- 3)= -13; - 3(1 -3в)-12=12; 3х - 2=14;3х - 12=2х;2х+ х +2 =20

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вопрос

2y + 6 = 21 - 3y
2y + 3y = 21 - 6
5y = 15
y = 3

2 - c + 3c - 9 = -13
2c - c - 9 = -13 + 2
c - 9 = -11
c = -2

-3(1 - 3b) - 12 = 12
-3 + 9b - 12 = 12
9b - 15 = 12
9b = 27
b = 3

3x - 2 = 14
3x = 16
x = 16/3

3x - 12 = 2x
3x - 2x = 12
x = 12

2x + x + 2 = 20
3x + 2 = 20
3x = 18
x = 18/3
x = 6

Проверено:

2(3) + 6 = 21 - 3(3)
6 + 6 = 21 - 9
12 = 12

2 - (-2) + 3(-2) - 9 = -13
2 + 2 - 6 - 9 = -13
-1 - 9 = -13
-10 = -13

-3(1 - 3(3)) - 12 = 12
-3(1 - 9) - 12 = 12
-3(-8) - 12 = 12
24 - 12 = 12
12 = 12

3(6) - 2 = 14
18 - 2 = 14
16 = 14

3(12) - 12 = 2(12)
36 - 12 = 24
24 = 24

2(6) + 6 + 2 = 20
12 + 6 + 2 = 20
20 = 20

Все уравнения верно решены.