Bonsoir,
Dévélopper:
A = (7x - 3)(7x + 3) - (7x + 3)²
⇒ identités remarquables:
- (a - b)(a + b) = a² - b²
- (a + b)² = a² + 2ab + b²
A = (7x)² - 3² - [(7x)² + 2*7x*3 + 3²)
A = 49x² - 9 - (49x² + 42x + 9)
A = 49x² - 9 - 49x² - 42x - 9
A = -42x - 18
Factoriser:
A = (7x - 3)(7x + 3) - (7x + 3)²
A = (7x - 3)(7x + 3) - (7x + 3)(7x + 3)
A = (7x + 3)(7x - 3 - (7x + 3))
A = (7x + 3)(7x - 3 - 7x - 3)
A = -6(7x + 3)
Bonne soirée.
