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## Homework Statement

http://img20.imageshack.us/img20/112/41590752.jpg [Broken]

## Homework Equations

## The Attempt at a Solution

I have no idea how to convert the left equation into the right one.

Could someone show me how to do that?

I don't understand why the right equation should be multiplied by 1/2

It is really giving me a headache.

Thanks for reading this post.

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