( 3y -1/y ) ^5
\[(-1/y)^5 + 5 \times (-1/y)^4 \times 3y \]........ and so on. see if you can do the rest.
For more info on this subject you can look here: http://en.wikipedia.org/wiki/Pascal's_triangle
http://www.krysstal.com/binomial.html This is better
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