Question

Tìm x

a) 8<\(2^x\le2^9.2^{-5}\) b) 27<\(81^3:3^x< 243\)

Answer 1

\(8< 2^x\le2^9.2^{-5}\)

\(\Leftrightarrow2^3< 2^x\le2^9.\dfrac{1}{2^5}\)

\(\Leftrightarrow2^3< 2^x\le2^4\)

\(\Leftrightarrow x=4\)

Vậy \(x=4\)

\(27< 81^3:3^x< 243\)

\(\Leftrightarrow3^3< \left(3^4\right)^3:3^x< 3^5\)

\(\Leftrightarrow3^3< 3^{12}:3^x< 3^5\)

\(\Leftrightarrow3^3< 3^{12-x}< 3^5\)

\(\Leftrightarrow3^{12-x}=3^4\)

\(\Leftrightarrow12-x=4\)

\(\Leftrightarrow x=4\)

Vậy \(x=4\)

Answer 2

Vội quá , nhầm :

Sửa lại :

b ) \(x=8\)