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Question
Square of 9x – 7xy is ______.
Options
81x2 + 49x2y2
81x2 – 49x2y2
81x2 + 49x2y2 – 126x2y
81x2 + 49x2y2 – 63x2y
Solution
Square of 9x – 7xy is 81x2 + 49x2y2 – 126x2y.
Explanation:
Square of (9x – 7xy) = (9x – 7xy)2
Comparing with (a – b)2, we get a = 9x and b = 7xy
(9x – 7xy)2 = (9x)2 – 2 · 9x · 7x + (7xy)2 ...[Using the identity, (a – b)2 = a2 – 2ab + b2]
= 81x2 – 126x2y + 49x2y2
= 81x2 + 49x2y2 – 126x2y
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