bonjour
pour b = 1/2 , 4 b² + 1 = 4 ( 1/2)² + 1 = 4 *1/4 + 1 = 4/4 + 1 = 4/4 + 4/4 = 2
4 b² + 1 = 2
4 b² + 1 - 2 = 0
4 b² - 1 = 0
( 2 b + 1) ( 2 b - 1) = 0 ⇔ b = - 1/2 ou 1/2
A = (5 + x ) ( 2 x - 1) = 10 x - 5 + 2 x² - x = 2 x² + 9 x - 5
( n - 1) ( n + 1) + 1 = n² - 1 + 1 = n ²