The (r+1)th term: $T_{r+1}$ = C(n, r) * $x^{n-r}$ * $y^r$.

Critical point: The subscript is r+1, not r. So $T_1$ = C(n,0)$x^n$, $T_2$ = C(n,1)$x^{n-1}$*y, etc.

To find the coefficient of a specific power: write the general term, set the exponent of the variable to the required value, solve for r, and compute C(n,r).

For ($ax^p$ + b/$x^q$)^n: $T_{r+1}$ = C(n,r) * ($ax^p$)^{n-r} * (b/$x^q$)^r = C(n,r) * $a^{n-r}$ * $b^r$ * $x^{p(n-r) - qr}$.