Question

4th term of (4x-y)^9

Answer 1

Now, let's do the same as we did for the previous one here.

$\bf (4x-y)^9\implies \begin{array}{llll} term&coefficient&value\\ -----&-----&-----\\ 1&+1&(4x)^9(-y)^0\\ 2&+9&(4x)^8(-y)^1\\ 3&+36&(4x)^7(-y)^2\\ 4&+84&(4x)^6(-y)^3 \end{array}$

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.