Bonjour j’aimerai de l’aide sur cette exercice svp. (7x-3)(7x+3)-(7x+3)^2

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.