Cho \(a=\log_25\). Biểu thức \(\log_41250\) bằng
\(2\left(1+4a\right)\). \(\dfrac{1+4a}{2}\). \(\dfrac{1-4a}{2}\). \(2\left(1-4a\right)\). Hướng dẫn giải:\(\log_41250=\log_{2^2}\left(2.5^4\right)=\frac{1}{2}\log_2\left(2.5^4\right)\)
\(=\dfrac{1}{2}\left[\log_22+4\log_25\right]=\dfrac{1}{2}\left(1+4a\right)\).