Factorise the following expression:
7a2 + 14a
∵ 7a2 = 7 × a × a = (7 × a) × a
14a = 2 × 7 × a = (7 × a) × 2
∴ 7a2 + 14a = (7 × a)[a+2]
= 7a(a+2)