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Question
Expand the following, using suitable identity:
(3a – 7b – c)2
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Solution
It is known that,
(x + y + z)2 = x2 + y2 + z2 + 2xy + 2yz + 2zx
(3a – 7b – c)2 = (3a)2 + (–7b)2 + (–c)2 + 2(3a)(–7b) + 2(–7b)(–c) + 2(–c)(3a)
= 9a2 + 49b2 + c2 – 42ab + 14bc – 6ac
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