Find a if the coefficients of `x^2`and `x^3`in the expansion of `(3+a x)^9`are equal.

Explanation

To solve the problem of finding the value of \( a \) such that the coefficients of \( x^2 \) and \( x^3 \) in the expansion of \( (3 + ax)^9 \) are equal, we can follow these steps:

### Step 1: Identify the General Term
The general term \( T_{r+1} \) in the expansion of \( (3 + ax)^n \) is given by:
\[ T_{r+1} = \binom{n}{r} (3)^{n-r} (ax)^r \]
For our case, \( n = 9 \), so:
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