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## Homework Statement

Find the coefficient of x

^{8}in the expansion of (x

^{2}-3)

^{7}

## Homework Equations

This one:

(n n-j) a

^{n-j}x

^{j}

## The Attempt at a Solution

Hi!

Well, I know that

x= x

^{2}

a= -3

n= 7

and apparently, j=8.

This is what confuses me. n-j is a negative number.. how would that even work?? My guess is that the x

^{2}has to do with it somehow... I'm thinking because the x is squared, then n wouldn't be 7.

Please help!

I wrote this on wolfram alpha because I was like.. "is this possible or is it just a typo?" and it gave me an answer!

Thank you!