;-; such confuse

2x/3(y^-1) --> You can move the y^-1 on top --> 2xy/3.

I just did a page of LaTex for this (which I lost) and I am not going to repeat it BUT

Here is a page that I put together on negative indices.  It should help you understand how it works.

http://web2.0calc.com/questions/indices-especially-negative-indices

Very simplistically,

If something is raised to a negative indice you swap it to the other side of the fraction line and change the negative index to a positive index.

Also do you mean

2x/3(y^-1)   which means     $$\frac{2x}{3}\times y^{-1}$$

or do you mean

2x/(3(y^-1))  which means   $$\frac{2x}{3y^{-1}}$$

You need to learn to use brackets so that your meaning is unmistakable!