now, let's do the same as we did for the previous one here.
[tex]\bf (4x-y)^9\implies
\begin{array}{llll}
term&coefficient&value\\
-----&-----&-----\\
1&+1&(4x)^9(-y)^0\\
2&+9&(4x)^8(-y)^1\\
3&+36&(4x)^7(-y)^2\\
4&+84&(4x)^6(-y)^3
\end{array}[/tex]
notice again, how did we get 84 for the 4th element's coefficient? well 36 * 7 / 3. and so on. And you can just expand it from there.
