'6 choose 4' is how it's read
\(\left(\begin{array}{ccc}n\\k\end{array}\right)\)=\(\frac{n!}{k!(n-k)!}\)
so
\(\left(\begin{array}{ccc}6\\4\end{array}\right)\)=\(\frac{6!}{4!(6-4)!}\)=\(\frac{720}{24(2)!}\)=\(\frac{720}{48}\)=15
that means the coeficient of the 5th term is 15
or remember that
\(\left(\begin{array}{ccc}n\\k\end{array}\right)\) is for a binomial to the nth power, to find the k+1 term
so
4+1=5
look at row coresponding to 6th power (7th row from top)
cound 5 from left to right
get 15
15(a)^1(b)^5 is 5th term in binomial (a+b)^6
