Question

Factorise the following algebraic expression by using the identity a² – b² = (a + b)(a – b)

25a² – 49b²

Answer 1

25a² – 49b² = 5²a² – 7²b²

= (5a)² – (7b)²

let a = 5a and b = 7b

a² – b² = (a + b)(a – b)

(5a)² – (7b)² = (5a + 7b)(5a – 7b)

25a² – 49b² = (5a + 7b)(5a – 7b)