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( 5 x + 2 ) ( 8 x - 1 ) = 0
soit 5 x + 2 = 0 → x = - 2/5
soit 8 x - 1 = 0 → x = 1/8
( 8 x + 20) - ( 10 x - 30 ) = 0
8 x + 20 - 10 x + 30 = 0
- 2 x + 50 = 0
- 2 x = - 50
x = 25
6 x² + 10 x + 18 x + 30 = 6 x² - 15 x + 6 x - 15
6 x² + 28 x + 30 = 6 x² - 9 x - 15
6 x² - 6 x² + 28 x + 9 x = - 15 - 30
37 x = - 45
x = - 45/37
15 x + 8 = 9 x - 4
15 x - 9 x = - 4 - 8
6 x = - 12
x = - 2