Bonjour

1)

(x + 6)² = x² + x * 6 * 2 + 6 * 6 = x² + 12x + 36

(a - 7)² = a² + a *- 7 * 2 + (- 7)² = a²- 14a + 49

(x - 3) (x + 3) = x * x - 3 * 3 = x² - 3² = x² - 9

2)

a. (5y + 4)² = (5y)² + 2 * 5y * 4 + 4² = 25y² + 40y + 16

b. (3b - 5)² = (3b)² - 5 * 3b * 2 + (- 5)² = 9b² - 30b + 25

c. (7 + 9x) (7 - 9x) = 7² - (9x)² = 49 - 81x².