Factorize:

a² + 11b + 11ab + a

Given a² + 11b + 11ab + a =(a × a + a × 1 + (11b) × 1 + (11b) × a)

Taking a common from 1^st and 2^nd term and (11b) from 3^rd and 4^th,

⇒ a² + 11b + 11ab + a = a (a + 1) + (11b)(1 + a)

⇒ a² + 11b + 11ab + a = (a + 1)(a + 11b)