Question

factorise 4x×x -5y×y

Answer 1

$4 {x}^{2} - 5 {y}^{2} \\ = {(2x)}^{2} - {(y \sqrt{5} )}^{2} \\ = (2x - y \sqrt{5} ) (2x + y \sqrt{5} ) \\ as \\ {x}^{2} - {y}^{2} = (x + y)(x - y)$

Answer 2

using (a.a_b.b)=(a+b)(a-b)
= 4x. x_5x.x
= (4x +5x)(4x _5x)