how to get from $x<x^2 + y^2$ to $\left(\frac12\right)^2<\left(x-\frac12\right)^2 +y^2$?

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How to get from $x<x^2 + y^2$ to $\left(\frac12\right)^2<\left(x-\frac12\right)^2 +y^2$?

This is were I saw it: Sketch all points in the complex plane such that $\mathrm{Re}(1/z)<1$

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Add on both sides $1/4$:

$${1\over 4}<{1\over 4} -x+x^2+y^2$$ so $$ \big({1\over 2}\big)^2<(x-{1\over 2})^2+y^2$$