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