bjr
tu sais que (a-b)² = a² - 2ab + b²
donc
(11a - 2b)² = (11a)² - 2*11a*2b + (2b)² = 121a² - 44ab + 4b²
(2x + 5)(5x - 3) = 2x*5x + 2x*(-3) + 5*5x + 5*(-3) = 10x² - 6x + 25x - 15
= 10x² + 19x - 15
(9x + 7)(9x - 7)
comme (a+b) (a-b) = a² - b²
on aura = (9x)² - 7² = 81x² - 49
(1 + x)² - (1 - x)² = 1² + 2x + x² - (1² - 2x + x²)
= 1 + 2x + x² - 1 + 2x - x² = 4x
