Consider the proof at page 2 found here: https://people.orie.cornell.edu/dpw/orie6334/Fall2016/lecture7.pdf
I cant wrap my head around the 2nd and third line:
\begin{align} &= \sum_{i \in V}x(i)^2 - \sum_{(i, j) \in E}\frac{2x(i)x(j)}{\sqrt{d(i)d(j)}}\\ &= \sum_{(i, j) \in E}(\frac{x(i)}{\sqrt{d(i)}} - \frac{x(j)}{\sqrt{d(j)}})^2 \end{align}
How did they go from the first line above to the second, what are the intermediate steps?
