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

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Answer 1 · 2016-02-21T20:43:29

Using the Binomial theorem which is formal expression is

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where

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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#