bonjour
A = 4 x² - 81 + (x - 4 ) ( 2 x + 9 )
A = 4 x² - 81 + 2 x² + 9 x - 8 x - 36
A = 6 x² + x - 117
2. 4 x² -81 = ( 2 x + 9 ) ( 2 x - 9 )
( 2 x + 9 )( 2 x - 9 )+ ( x- 4 )( 2 x + 9 )
= ( 2 x + 9 ) ( 2 x -9 + x - 4)
= ( 2 x + 9 )( 3 x - 5 )
pour x = 13/3
= ( 26/3 + 9 ) ( 39/3 - 5 )
= ( 26/3 + 27/3 ) ( 39/3 - 15 /3 )
= 53/3 * 24/3
= 1 272/9 = 424/3