jika 7 log 3 = a dan 3log 4 = b tentukan nilai 6log 686

karena [tex]^7\log{3}=a[/tex] dan [tex]^3\log{4}=b\Leftrightarrow 2\cdot^3\log{2}=b\Leftrightarrow ^3\log{2}=\frac{b}{2}[/tex], maka
[tex]^6\log{686}=\frac{^3\log{686}}{^3\log{6}}=\frac{^3\log{(2\cdot7^3)}}{^3\log{(2\cdot3)}}=\frac{^3\log{2}+3\cdot^3\log{7}}{^3\log{2}+^3\log{3}}=\frac{b+3\cdot\frac{1}{a}}{b+1}\cdot\frac{a}{a}=\frac{ab+3}{ab+a}[/tex]