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If the coefficients of the second, third and fourth terms in the expansion of (1 + x)n  are in AP, show that n = 7.

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According to the question, nC1⋅ nC2⋅ nC3 are in AP. So,

Since, the symbol nC3 demands that n should be ≥3.

So, n cannot be 2. Therefore, n = 7.

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