Find the seventh
term^{ }of (2a+b)^{9}.

Recall that the
(r+1)th term is _{n}C_{r}x^{n-r}y^{r}, so r is
one less than the number of the term you are looking for. So, to find the 7^{th}
term, use r=6, n=9, x=2a, y=b:

_{9}C_{6}(2a)^{9-6}b^{6}=2^{3}a^{3}b^{6}=84(2^{3})a^{3}b^{6}=672a^{3}b^{6}