Question

Use a suitable identity to get each of the following products.

(i) (7a − 9b) (7a − 9b)

(ii) (− a + c) (− a + c)

Answer 1

(i) (7a − 9b) (7a − 9b) = (7a − 9b)²

= (7a)² − 2(7a)(9b) + (9b)² [(a − b)² = a² − 2ab + b²]

= 49a² − 126ab + 81b²

(ii) (− a + c) (− a + c) = (− a + c)2

= (− a)² + 2(− a) (c) + (c)² [(a + b)² = a² + 2ab + b²]

= a² − 2ac + c²