How do you calculate log_6 5log65 with a calculator?

1 Answer
Aug 12, 2016

log_6 5 = log 5 / log 6 ~~ 0.8982444log65=log5log60.8982444

Explanation:

Use the change of base formula:

log_a b = (log_c b) / (log_c a)logab=logcblogca

So you can use natural or common logs:

log_6 5 = ln 5 / ln 6log65=ln5ln6

log_6 5 = log 5 / log 6log65=log5log6

In fact, if you know log 2 ~~ 0.30103log20.30103 and log 3 ~~ 0.47712log30.47712 then you can get a reasonable approximation with basic arithmetic operations:

log_6 5 = log 5 / log 6 = (log 10 - log 2) / (log 2 + log 3)log65=log5log6=log10log2log2+log3

~~ (1-0.30103)/(0.30103+0.47712) = 0.69897/0.77815 ~~ 0.8982510.301030.30103+0.47712=0.698970.778150.89825

Actually the true value is closer to 0.89824440.8982444