View Full Version : Help me with my logarithm question
kwarr5
Mar 18, 2011, 01:39 PM
solve log5(x-4)=log7(x) for x.
5 and 7 are bases.
HELP!
ebaines
Mar 18, 2011, 02:52 PM
To help get you started, use the rule for converting logarithm bases:
\log_a(b) = \frac {\log_c(b)} {\log_c(a)}
So to convert to a common logarithm base in the problemn you were given you can do this:
\log_7(x) = \frac {\log_5(x)}{\log_5(7)}
Now you can rewrite the original equation like this:
\log_5(x-4) = \frac {\log_5(x)}{\log_5(7)}\\
Can you take it from here?
kwarr5
Mar 18, 2011, 03:17 PM
well I get that.. I just don't understand where to take it from there the two x's are confusing me.
kwarr5
Mar 18, 2011, 03:17 PM
well I get that.. I just don't understand where to take it from there the two x's are confusing me
Unknown008
Mar 18, 2011, 11:57 PM
\log_5 7
Can be worked out. Then, you end up with something like:
\log\ x = a\log\ y
Raise a to become y to the power of a, to get:
\log_5 7
Can be worked out. Then, you end up with something like:
\log\ x = \log\ y^a
Now, can you continue?