# Thread: Binomial Expansion

1. ## Binomial Expansion

The question is:

Which term in the expansion of ( [1/3x^2] - x )^15 is the constant term?

Sorry about not creating the equation properly.

Could anyone provide a moderately in-depth answer and how to approach the question?

2. ## Re: Binomial Expansion

Is this $\displaystyle \displaystyle \left( \frac{1}{3}x^2 - x \right) ^{15}$ or $\displaystyle \displaystyle \left( \frac{1}{3x^2} - x \right) ^{15}$?

3. ## Re: Binomial Expansion

The second one. Sorry for the trouble haha!

5. ## Re: Binomial Expansion

In the 5th line that you wrote, where does the [(-1)^r][x^r] come from? (-x)^15 ??
If so, how?

Other than that I seem to understand it though! Thanks for making that!!!

*edit
NVM It seems there was a mistake but I know what happened now! Thanks for the solution. +rep

6. ## Re: Binomial Expansion

It is a typing error. It should be (-x)^r= (-1)^r * x^r