Question

Using the identity (x + a)(x + b) = x² + x(a + b) + ab, find the following product

(6a + 9)(6a – 5)

Answer 1

(6a + 9)(6a – 5)

Substituting x = 6a, a = 9 and b = – 5

In (x + a)(x + b) = x² + x(a + b) + ab, we get

(6a + 9)(6a – 5) = (6a)² + 6a(9 + (– 5)) + (9 × (– 5))

6²a² + 6a(4) + (– 45)

= 36a² + 24a – 45

(6a + 9)(6a – 5) = 36a² + 24a – 45