bonjour
A = 5 x² - 40 x + x² - x + 2 x - 2
= 6 x² - 39 x - 2
B = 25 x² + 20 x + 4 - 3 x - 3
= 25 x² + 17 x + 1
C = 25 x² - 1 - ( 6 x² - 24 x + 5 x - 20 )
= 25 x² - 1 - 6 x² + 24 x - 5 x + 20
= 19 x² + 19 x + 19
2 x² - 3 = - 7
2 x² = - 7 + 3
2 x² = - 4
pas de solution, un carré est toujours positif
( x + 7 ) ( 3 x - 5 ) = 5 x ( x + 7 )
( x + 7 ) ( 3 x - 5 ) - 5 x ( x + 7 ) = 0
( x + 7 ) ( 3 x - 5 - 5 x ) = 0
( x + 7 ) ( - 2 x - 5 ) = 0
x = - 7 ou - 5/2
( 2 x + 3 ) / ( x + 5 ) = 1
2 x + 3 = x + 5
2 x - x = 5 - 3
x = 2
