chỉ e cách làm bài này ạ
\(log_4\left(3^x-1\right).log_{\dfrac{1}{4}}\dfrac{3^x-1}{16}\le\dfrac{3}{4}\)
\(\Leftrightarrow log_4\left(3^x-1\right).\left(-log_4\dfrac{3^x-1}{16}\right)\le\dfrac{3}{4}\)
\(\Leftrightarrow log_4\left(3^x-1\right).\left(2-log_4\left(3^x-1\right)\right)\le\dfrac{3}{4}\)
Đặt \(log_4\left(3^x-1\right)=a\)
\(\Rightarrow a\left(2-a\right)\le\dfrac{3}{4}\)
\(\Leftrightarrow\left[{}\begin{matrix}a\le\dfrac{1}{2}\\a\ge\dfrac{3}{2}\end{matrix}\right.\)
Làm tiếp nhé
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