The coefficients of three consecutive terms in the expansion of `(1+a)^n`are in the ratio 1: 7 : 42. Find n.

Explanation

To solve the problem, we need to find the value of \( n \) given that the coefficients of three consecutive terms in the expansion of \( (1 + a)^n \) are in the ratio \( 1:7:42 \).

### Step 1: Understand the General Term in the Expansion
The general term in the expansion of \( (1 + a)^n \) is given by:
\[ T_{r+1} = \binom{n}{r} a^r \]
where \( \binom{n}{r} \) is the binomial coefficient representing the coefficient of the term.
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