bonjour
1. ( x + 7 )² - 3 ( x + 7) = 0
( x + 7) ( x + 7 - 3 ) = 0
( x + 7) ( x + 4 ) = 0
soit x + 7 = 0 ⇔ x = - 7
soit x + 4 = 0 ⇔ x = - 4
S ( - 4 ; - 7 )
2. ( 2 x - 1 )² - 9 = 0
( 2 x - 1 - 3 ) ( 2 x - 1 + 3 ) = 0
( 2 x - 4 ) ( 2 x + 2 ) = 0
soit 2 x-4 = 0 ⇔ 2 x = 4 ⇔ x = 2
soit 2 x + 2 = 0 ⇔ 2 x = - 2 ⇔ x = - 1
S ( 2 ; - 1 )
3. 25 x² - 4 - ( 2 x + 3) ( 5 x + 2 ) = 0
( 5 x - 2 ) ( 5 x + 2) - ( 2 x + 3 ) ( 5 x + 2) = 0
( 5 x + 2) ( 5 x - 2 - 2 x - 3 ) = 0
( 5 x + 2 ) ( 3 x - 5 ) = 0
soit 5 x + 2 = 0 ⇔ 5 x = - 2 ⇔ x = - 2/5
soit 3 x - 5 = 0 ⇔ 3 x = 5 ⇔ x = 5/3
S ( - 2/5 ; 5/3 )
5. x² = 20
x = √20 ou - √20 car ( √20)² = 20 et ( - √20)² = 20
