Question

How do you use the Change of Base Formula and a calculator to evaluate the logarithm `log_9 2.15`?

Answer 1

I found: `0.3483`

Explanation:

The Change of Base Formula allows you to write:

`log_ab=(log_cb)/(log_ca)`
and change your base from `a` to the new base `c`.

We can choose, as new base, `e` and use natural logs, `ln`, that can be evaluated using a pocket calculator and get:

`log_9(2.15)=(ln2.15)/(ln9)=0.3483`