Exo 1
(4-5x)² - (4-5x)(4+5x) = 5x( 10x - 8)
(4-5x)(4-5x) - (4-5x)(4+5x) = 50x² - 40x
16 - 20x - 20x + 25x² - [ (4-5x)(4+5x) ] = 50x² - 40x
16 - 20x - 20x + 25x² - [ 16 +20x - 20x - 25x² ] = 50x² - 40x
16 - 40x + 25x² - [ 16 - 25x² ] = 50x² - 40x
16 - 40x + 25x² - 16 + 25x² = 50x² - 40x
-40x + 50x² = 50x² - 40x
Exo 2
1) A= 16x²-9
(4x)² - 3²
(4x - 3)(4x+3)
2) On ne voit pas entièrement le calcul !
