Bonjour !
1. (x + 14)(x - 14) = x² - 14² = x² - 196
2. (7x + 9)(7x - 9) = (7x)² - 9² = 49x² - 81
3. (2/3 + x/4)(2/3 - x/4) = (2/3)² - (x/4)² = 4/9 - x²/8
4. (z + 7/4)(z - 35/20) = (z + 7/4)(z - 5*7/4) = z² - (7/4)² = z² - 49/16
J'espère t'avoir aidé. Bon courage !
