# Expansion of (x-(3/x^2)^9

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• May 12th 2010, 11:08 AM
acc
Expansion of (x-(3/x^2)^9
In the expansion of (x-(3/x^2)^9 find the following:

a) the term containing x6

b) the constant term

This is my last question, I swear! :P
• May 12th 2010, 08:53 PM
mr fantastic
Quote:

Originally Posted by acc
In the expansion of (x-(3/x^2)^9 find the following:

a) the term containing x6

b) the constant term

This is my last question, I swear! :P

The general term is ${9 \choose r} x^{9 - r} \left( -\frac{3}{x^2}\right)^r = {9 \choose r} (-3)^r x^{9 - r} x^{-2r} = {9 \choose r} (-3)^r x^{9 - 3r}$.

a) You require the coefficient of the power of x corresponding to 9 - 3r = 6.

b) You require the coefficient of the power of x corresponding to 9 - 3r = 0.