Question

What is the 5th term of `(s + t)^9`?

Answer 1

Using the Binomial theorem which is formal expression is

where

we have that

`(s+t)^9=s^9+9 s^8 t+36 s^7 t^2+84 s^6 t^3+126 s^5 t^4+126 s^4 t^5+84 s^3 t^6+36 s^2 t^7+9 s t^8+t^9`

hence the 5th term is `126s^5t^4`