(i) 78 × 82 = (80 − 2) (80 + 2)
= (80)2 − (2)2
= 6400 − 4 = 6396
Note : [(a + b) (a − b) = a2 − b2]
(ii) 8.92 = (9.0 − 0.1)2
= (9.0)2 − 2(9.0) (0.1) + (0.1)2
= 81 − 1.8 + 0.01 = 79.21
Note : [(a − b)2 = a2 − 2ab + b2 ]
(iii) 1.05 × 9.5 = 1.05 × 0.95 × 10
= (1 + 0.05) (1− 0.05) ×10
= [(1)2 − (0.05)2] × 10
= [1 − 0.0025] × 10
= 0.9975 × 10 = 9.975
Note : [(a + b) (a − b) = a2 − b2]