Explications étape par étape

( 2 - 3x ) + ( 6x - 1 ) = 2 - 3x + 6x - 1 = 1 + 3x

( 6x - 1 ) + ( - 4x - 1 ) = 6x - 1 - 4x - 1 = 2x - 2

( - 4x - 1 ) + ( 5 - 3x ) = - 4x - 1 + 5 - 3x = - 7x + 4

( 1 + 3x ) + ( 2x - 2 ) = 1 + 3x + 2x - 2 = - 1 + 5x

( 2x - 2 ) + ( - 7x + 4 ) = 2x - 2 - 7x + 4 = - 5x + 2

( - 1 + 5x ) + ( - 5x + 2 ) = 1

- 1 + 5x - 5x + 2 = 1

1 = 1