Question

[linhlucy]

bài 6 : tìm x :

câu 9, \(3^x=9^{-6}.27^{-5}.81^8\)

câu 18, \(4^{x+3}-3.4^{x+1}=13.4^{11}\)

Answer 1

[Nguyễn Lê Phước Thịnh]

Câu 9: 

\(3^x=9^{-6}\cdot27^{-6}\cdot81^8\)

\(\Leftrightarrow3^x=\dfrac{1}{9^6\cdot27^6}\cdot81^8=\dfrac{1}{3^{12}\cdot3^{18}}\cdot3^{32}=3^2\)

=>x=2

Câu 18:

\(4^{x+3}-3\cdot4^{x+1}=13\cdot4^{11}\)

\(\Leftrightarrow4^x\cdot64-3\cdot4^x\cdot4=13\cdot4^{11}\)

\(\Leftrightarrow4^x\left(64-3\cdot4\right)=13\cdot4^{11}\)

\(\Leftrightarrow4^x=13\cdot4^{10}\cdot4:52=4^{10}\)

=>x=10