Question

Tính giá trị các biểu thức sau:

a) \({\log _{\frac{1}{4}}}8\);                             

b) \({\log _4}5.{\log _5}6.{\log _6}8\).

Answer 1

a: \(log_{\dfrac{1}{4}}8=log_{2^{-2}}2^3=\dfrac{-3}{2}\cdot log_22=-\dfrac{3}{2}\)

b: \(log_45\cdot log_56\cdot log_68\)

\(=log_45\cdot\dfrac{log_46}{log_45}\cdot\dfrac{log_48}{log_46}\)

\(=log_48=log_{2^2}2^3=\dfrac{3}{2}\)