regarding $\displaystyle{d(x, y) = \sqrt{\sum_{i=1}^{n}{(x_i - y_i)^2}}}$ for distance calculations

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Since $\displaystyle{d(x, y) = \sqrt{\sum_{i=1}^{n}{(x_i - y_i)^2}}}$, $d(A, B)$ should be $2\sqrt{2}$ or I misunderstood something?

By the way, how to run this locally after checking it out?