Answer:
[tex]5^{th} term = 126a^5b^4[/tex]
Step-by-step explanation:
[tex]\left(a+b\right)^n=\sum _{i=0}^n\binom{n}{i}a^{\left(n-i\right)}b^i\\\\(a + b)^9 =\sum _{i=0}^9\binom{9}{i}a^{\left(9-i\right)}b^i\\\\[/tex]
[tex]=a^9 + 9a^8b + 36a^7b^2 + 84a^6 b^3 + 126a^5b^4+ 126a^4b^5+84a^3b^6+ 36a^2b^7+ 9ab^8+b^9[/tex]
[tex]5^{th} term = 126a^5b^4[/tex]
