bonjour
x² + 3 x = 28
x² + 3 x - 28 = 0
Δ = 9 - 4 ( 1 * - 28) = 9 + 112 = 121
x ₁ = ( - 3 + 11) / 2 = 8/2 = 4
x ₂ = ( - 3 - 11)/2 = - 14/2 = - 7
S { - 7 ; 4 }
2 x² + 7 x + 3 = - 2
2 x² + 7 x + 3 + 2 = 0
2 x² + 7 x + 5 = 0
Δ = 49 - 4 ( 2 * 5) = 49 - 40 = 9
x 1 = ( - 7 + 3)/ 4 = - 4/4 = - 1
x 2 = ( - 7 - 3)/4 = - 10/4
S { - 10/4 , - 1 }
( x - 4 ) x = 21
x² - 4 x - 21 = 0
Δ = ( - 4 )² - 4 ( 1 * - 21) = 16 + 84 = 100
x 1 = ( 4 + 10) / 2 = 14/2 = 7
x 2 = ( 4 - 10 )/ 2 = - 6 /2 = - 3
S { - 3 ; 7 }
5 x² + 4 - 2 x ( x + 2) = 5 ( x + 1) - 2 x - 1
5 x² + 4 - 2 x² - 4 x = 5 x + 5 - 2 x - 1
3 x² - 4 x - 5 x + 2 x = - 4 + 5 - 1
3 x² - 7 x = 0
x ( 3 x - 7 ) = 0
soit x = 0
soit 3 x - 7 = 0 et x = 7/3
S { 0 ; 7/3 }
je te laisse continuer
