1. ## log 45

If log 3 = x and log 5 = y, then rewrite log 45.

2. Originally Posted by magentarita
If log 3 = x and log 5 = y, then rewrite log 45.
45 = 3x3x5

log(ab^2) = 2log(b) + log(a)

3. ## are you.....

Originally Posted by e^(i*pi)
45 = 3x3x5

log(ab^2) = 2log(b) + log(a)
Are you saying for me to use the given formula?

4. Originally Posted by magentarita
Are you saying for me to use the given formula?
Yup, in this case:

$log(45) = log(9) + log(5) = \log(3^2) + log(5) = 2log(3) + log(5)$

Since you have log(3) = x and log(5) is y you will get $log(45) = 2x +y$

5. Originally Posted by magentarita
Are you saying for me to use the given formula?
You should have recognized this "formula" as an application of the basic log rules. (That is, they were supposed to have taught you the log rules before assigning this exercise.)

To learn how to expand and "compress" log expressions as demonstrated in this and other threads, try here.

6. ## ok

Originally Posted by e^(i*pi)
Yup, in this case:

$log(45) = log(9) + log(5) = \log(3^2) + log(5) = 2log(3) + log(5)$

Since you have log(3) = x and log(5) is y you will get $log(45) = 2x +y$
I clearly see the substitution for log3 and log5 now.

7. ## help

the rules of logarithms are such that log(ab) = log a + log b
log(a/b) = log a - log b
$log (a^b) = b \times log (a)$