Math Help - Coeffcient in an Expansion

1. Coeffcient in an Expansion

In the expansion of (x2 – x)8 find the coefficient of x8.

2. Well, do it! What is your plan?

$
(x^{2}-x)^{8} = \left(x^{2}\right)^{8} + 8\left(x^{2}\right)^{7}(-x) + ...???$

Fill in the ??? and pick out the right one. You can learn to write down specific terms as your NEXT assignment.

Of course, it might be easier on this one...

$x^{8}\cdot (x - 1)^{8} = x^{8}\cdot\left[x^{8} + 8x^{7}(-1) + ...???\right]$

3. Originally Posted by acc
In the expansion of (x2 – x)8 find the coefficient of x8.
The general term is ${8 \choose r} (x^2)^{8 - r} (-x)^r = {8 \choose r} (-1)^r x^{16 - r}$. You require the coefficient of the power of x corresponding to 16 - r = 8 ....