Bonjour,
a) (a + b)² = a² + 2ab + b²
(7x + 1)² - 2 (x + 4x²)
= (7x)² + 2*7x*1 + 1² - 2 * x - 2 * 4x²
= 49x² + 14 + 1 - 2x - 8x²
= 49x² - 8x² - 2x + 14 + 1
= 41x² - 2x + 15
b) (a - b)² = a² - 2ab + b²
(x - √5)²
= x² - 2 * x * √5 + (√5)²
= x² - 2√5x + 5
c) (a - b)(a + b) = a² - b²
(x/7 - 2/3)(x/7 + 2/3)
= (x/7)² - (2/3)²
= x²/49 - 4/9
N'hésite pas si tu as des questions !
