I know this isn't strictly a Pre-Uni question, but it only involves basic algebra as far as I can tell.

Given the following picture:

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I don't understandwhy$\displaystyle (x_1-x_2)^2 \ge 0 \implies P(n)~ \text{true for} ~n=2$.

I can seehowthey derived the simpler inequality through simple algebraic manipulation, but don't understand why it means the statement holds for n=2.