Question

Expand the following:

(5ab − 4cd)²

Answer 1

(5ab − 4cd)²

Using the identity:

(a − b)² = a² − 2ab + b²

Here, let a = 5ab, b = 4cd

Thus,

(5ab − 4cd)² = (5ab)² − 2(5ab)(4cd) + (4cd)²

= 25a²b² − 2(20abcd) + 16c²d²

∴ (5ab − 4cd)² = 25a²b² − 40abcd + 16c²d²