Find the `13^th` term in the expansion of
`(9x-1/(3sqrtx))^18`

Explanation

Let `(r+1)^ th ` term in the éxpansion of `(9 x-1/3 sqrtx)^18` is `T_r+1= ^18 C_r(9 x)^18-r(-1/3 sqrtx)^r`

`T_13=T_12+1= ^18 C_12(9 hatx)^18-12(-1/3 sqrtx)^12=18564 xx 9^9 xx x^6 xx 1/3^12 x^6=18564`