73nastya73

14х +21=21

14х=0

х=0

ну как-то так

1grom9

1способ:

7 ( 2х + 3 ) = 21

7 * 2х + 7 * 3 = 21

14х + 21 = 21

14х = 21 - 21

14х = 0

х = 0 : 14

х = 0

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2 способ:

7 ( 2х + 3 ) = 21

2х + 3 = 21 : 7

2х + 3 = 3

2х = 3 - 3

2х = 0

х = 0 : 2

х = 0