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:
http://img192.imageshack.us/img192/6616/math15.png
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I don't understand why $\displaystyle (x_1-x_2)^2 \ge 0 \implies P(n)~ \text{true for} ~n=2$.
I can see how they derived the simpler inequality through simple algebraic manipulation, but don't understand why it means the statement holds for n=2.