deletions | additions       diff --git a/untitled.tex b/untitled.tex  index 1cba934..6c1cc81 100644  --- a/untitled.tex  +++ b/untitled.tex 
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Notice the left hand side $$(x+\frac{1}{2}c)^2 + (y-\frac{1}{2}d)^2 \geq 0$$  Then the right hand side $$ -b + \frac{1}{4}(c^2+d^2)\geq 0.$$  Thus, $\frac{1}{4}(c^2+d^2)\geq b$  Hence, $(c^2+d^2)\geq 4b$  \end{proof}  \end{problem}