This is my doubt:

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

Thanks a lot. =)

*r*^{th }term in the expansion of (*b *+ *x*)^{n }is . The coefficient of

Here *b *= 3 and* x = ax*

According to the question coefficients of *x*^{2} and* x*^{3} are equal, then,

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