ĐKXĐ: \(x>0\)
\(\left(log_3x^5\right)^2-25.2.log_3x-750\le0\)
\(\Leftrightarrow\left(5log_3x\right)^2-50log_3x-750\le0\)
\(\Leftrightarrow25log_3^2x-50log_3x-750\le0\)
Đặt \(log_3x=t\)
\(\Rightarrow25t^2-50t-750\le0\)
\(\Rightarrow1-\sqrt{31}\le t\le1+\sqrt{31}\)
\(\Rightarrow1-\sqrt{31}\le log_3x\le1+\sqrt{31}\)
\(\Rightarrow3^{1-\sqrt{31}}\le x\le3^{1+\sqrt{31}}\)