Question

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

Answer 1

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.