`log_{12} 18 = a + b/(c + log_{2} 3)`
`text{Ta có}`
`log_{12} 18`
`= (log_{2} 18)/(log_{2} 12)`
`= (log_{2} (2.3^{2)))/(log_{2} (3.2^{2}))`
`= (log_{2} 2 + 2log_{2} 3)/(log_{2} 2^{2} + log_{2} 3)`
`= (1 + 2log_{2} 3)/(2 + log_{2} 3)`
`= (4 + 2log_{2} 3 - 3)/(2 + log_{2} 3)`
`= (2(2 + log_{2} 3))/(2 + log_{2} 3) + (-3)/(2 + log_{2} 3)`
`= 2 + (-3)/(2 + log_{2} 3) = a + b/(c + log_{2} 3)`
`->` \(\left\{ \begin{array}{l}a = 2\\b = -3\\c = 2\end{array} \right.\)
`-> a + b + c = 2 - 3 + 2 = 1`
