1.

Use a suitable identity to get each of the following products.(i) (7a − 9b) (7a − 9b)(ii) (− a + c) (− a + c)

Answer»

(i) (7a − 9b) (7a − 9b) = (7a − 9b)2

= (7a)2 − 2(7a)(9b) + (9b)2 [(a − b)2 = a2 − 2ab + b2]

= 49a2 − 126ab + 81b2

(ii) (− a + c) (− a + c) = (− a + c)2

= (− a)2 + 2(− a) (c) + (c)2 [(a + b)2 = a2 + 2ab + b2]

= a2 − 2ac + c2


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