Factorise: (2a+1)3+(a−1)3
(2a+1)3+(a–1)3=(2a+1+a−1)((2a+1)2+(a−1)2−(2a+1)(a−1))=(3a)(4a2+1+4a+a2+1−2a−2a2+2a−a+1)=(3a)(3a2+3a+3)=(9a)(a2+a+1)