Đặt:
\(L=\sqrt{a+2009}+\sqrt{b+2009}+\sqrt{c+2009}\)
\(L^2=\left(\sqrt{a+2009}+\sqrt{b+2009}+\sqrt{c+2009}\right)^2\)
\(\le\left(1^2+1^2+1^2\right)\left(a+b+c+6027\right)\) (bđt bunhiacopxki)
\(=3\left(2+6027\right)=18087\Leftrightarrow A\le\sqrt{18087}\)
p/s: đề đã fix vì t thấy số qá to:v