Ta có: VP=\(4\log_3^2a^{-1}-\log_3a^{-2}.\log{b^2}+\log_3^2{b}\)
\(=4\left [-\log_3a \right ]^2-(-2)\log_3a.2\log{b}+\log_3^2{b}\)
\(=4\log_3^2a +4\log_3a.\log{b}+\log_3^2{b}\)
\(=\left ( 2\log_3a+\log_3b \right )^2\)
\(=\left ( \log_3a^2+\log_3b \right )^2\)
\(=[ \log_3({a^2b )}]^2\)=VP
Vậy ta có đpcm