(i) (1.1m − 0.4) (1.1 m + 0.4)
= (1.1m)2 − (0.4)2 [(a + b) (a − b) = a2 − b2]
= 1.21m2 − 0.16
(ii) (a2 + b2) (− a2 + b2) = (b2 + a2) (b2 − a2)
= (b2)2 − (a2)2 [(a + b) (a − b) = a2 − b2]
= b4 − a4
(iii) (6x − 7) (6x + 7) = (6x)2 − (7)2 [(a + b) (a − b) = a2 − b2]
= 36x2 − 49