'6 choose 4' is how it's read
[tex] \left(\begin{array}{ccc}n\\k\end{array}\right) [/tex]=[tex] \frac{n!}{k!(n-k)!} [/tex]
so
[tex] \left(\begin{array}{ccc}6\\4\end{array}\right) [/tex]=[tex] \frac{6!}{4!(6-4)!} [/tex]=[tex] \frac{720}{24(2)!} [/tex]=[tex] \frac{720}{48} [/tex]=15
that means the coeficient of the 5th term is 15
or remember that
[tex] \left(\begin{array}{ccc}n\\k\end{array}\right) [/tex] 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
