If In The Expression Of (1 + x)m (1 – x)n. The Coefficient Of x and x2 are 3 And – 6 Respectively, Then m is

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Question

If in the expression of (1 + x)m (1 – x)n. the coefficient of x and x2 are 3 and – 6 respectively, then m is

Solution

Correct option is

12

m(m – 1) + n(n – 1) – 2mn = – 12

or (m – n)2 – (m + n) = – 12

or 9 – (2m – 3) = – 12    ∴ m = 12

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