SOLUTION: how do you condense a problem like {{{ log3-log4-log7 }}}?

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Question 171046: how do you condense a problem like +log3-log4-log7+?
Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!

The appropriate logarithm rules to apply are:

1. log%28b%2Cx%5B1%5D%29%2Blog%28b%2Cx%5B2%5D%29=log%28b%2C%28x%5B1%5D%2Ax%5B2%5D%29%29 and

2. log%28b%2Cx%5B1%5D%29-log%28b%2Cx%5B2%5D%29=log%28b%2C%28x%5B1%5D%2Fx%5B2%5D%29%29

First thing is to apply the Associative and Distributive Properties:

log%283%29-log%284%29-log%287%29=log%283%29-%28log%284%29%2Blog%287%29%29

Now, using Rule 1., you can render the part in parentheses as:

log%2828%29 and substitute, thus:

log%283%29-log%2828%29

Now apply rule 2., thus:

log%283%2F28%29

Since 3%2F28 is already reduced to lowest terms, you are done.

Check the reasonability of your answer with a calculator:

log%283%29+=+0.4771 (roughly)

log%284%29+=+0.6021 (roughly)

log%287%29+=+0.8451 (roughly)

0.4771+-+0.6021+=+-0.125 and -0.125+-+0.8451+=+-0.9701

So far, so good. Since log%2810%2C1%29=0, the log of something smaller than 1, in particular 3%2F28 must be less than zero.

Again, from the calculator: 3%2F28+=+0.1071 (roughly) and log%280.1071%29+=+-0.9072.

Close enough.