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(i) 78 × 82

(ii) 8.9

(iii) 1.05 × 9.5

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(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]

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