# Binomial Expansion

• Mar 19th 2013, 10:01 PM
Pourdo
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?
• Mar 19th 2013, 10:20 PM
Prove It
Re: Binomial Expansion
Is this $\displaystyle \displaystyle \left( \frac{1}{3}x^2 - x \right) ^{15}$ or $\displaystyle \displaystyle \left( \frac{1}{3x^2} - x \right) ^{15}$?
• Mar 19th 2013, 10:25 PM
Pourdo
Re: Binomial Expansion
The second one. Sorry for the trouble haha!
• Mar 20th 2013, 03:47 AM
ibdutt
Re: Binomial Expansion
• Mar 20th 2013, 10:26 AM
Pourdo
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
• Mar 20th 2013, 08:15 PM
ibdutt
Re: Binomial Expansion
It is a typing error. It should be (-x)^r= (-1)^r * x^r