Question

Find ‘a’ if the coefficients of x2 and x3 in the expansion of (3+)9 are equal

Answer 1

Step-by-step explanation:

In the expansion of (a+b)n the (r+1)th term is 

Tr+1=nCran−rbr

General term in (3+ax)9 is

Tr+1=9Cr39−r(ax)r=9Cr39−rarxr

Given that coefficient of x2=co-efficient of x3

⇒9C239−2a2=9C339−3a3

⇒a=9C339−39C239−2