Tìm gtnn của biểu thức P=a^2-a+2020

$\begin{array}{l}
P = {a^2} – a + 2010\\
P = {a^2} – 2.a.\dfrac{1}{2} + {\left( {\dfrac{1}{2}} \right)^2} + \left[ {2020 – {{\left( {\dfrac{1}{2}} \right)}^2}} \right]\\
P = {\left( {a – \dfrac{1}{2}} \right)^2} + \dfrac{{8079}}{4}\\
Vi\,\,{\left( {a – \dfrac{1}{2}} \right)^2} \ge 0\,\,\left( {\forall a} \right)\,\,nen\,\,\,{\left( {a – \dfrac{1}{2}} \right)^2} + \dfrac{{8079}}{4} \ge \dfrac{{8079}}{4}\left( {\forall a} \right)\,\,\\
\Rightarrow GTNN\,\,la\,\,\,\dfrac{{8079}}{4}
\end{array}$