x² – x(a + 2b) + 2ab

= x² – ax – 2bx + 2ab

= x² – 2bx – ax + 2ab

= (x² – 2bx) – (ax – 2ab)

= x(x – 2b) – a(x – 2b)

= (x – 2b)(x – a)

So we get,

x² – x(a + 2b) + 2ab = (x – 2b)(x – a)