SOLUTION: Arjun incorrectly writes log7 x+log7 y-log7 z as a single logarithm. log7 x + log7 y - log7 z = log7 (x+y=z) Where did Arjun make errors? Explain his errors and the properties of

Algebra ->  Exponential-and-logarithmic-functions -> SOLUTION: Arjun incorrectly writes log7 x+log7 y-log7 z as a single logarithm. log7 x + log7 y - log7 z = log7 (x+y=z) Where did Arjun make errors? Explain his errors and the properties of      Log On


   



Question 1189571: Arjun incorrectly writes log7 x+log7 y-log7 z as a single logarithm.
log7 x + log7 y - log7 z = log7 (x+y=z)
Where did Arjun make errors? Explain his errors and the properties of
logarithms that lead to the correct answer. State the correct answer.

please help, i beg you, please

Found 2 solutions by math_tutor2020, Edwin McCravy:
Answer by math_tutor2020(3817) About Me  (Show Source):
You can put this solution on YOUR website!

I think you meant to write
log7 x + log7 y - log7 z = log7 (x+y-z)

If so, then that equation is incorrect (or Arjun is incorrect in writing such an equation).

The log rules we'll use are
log(A) + log(B) = log(A*B)
log(A) - log(B) = log(A/B)
These rules are used frequently, so be sure to memorize them or have them handy on a flashcard somewhere.

Based on the first rule, we can say
log7 x + log7 y = log7 (x*y)

Then incoporating the second rule allows us to say
log7 (x*y) - log7 z = log7 (x*y/z)

In short, the original expression of
log7 x + log7 y - log7 z
becomes
log7 (x*y/z)

Side note: By writing "log7", it means "log base 7".


Answer by Edwin McCravy(20060) About Me  (Show Source):
You can put this solution on YOUR website!

Arjun incorrectly writes log7 x+log7 y-log7 z as a single logarithm.
log7 x + log7 y - log7 z = log7 (x+y=z)
Where did Arjun make errors? Explain his errors and the properties of
logarithms that leads to the correct answer. State the correct answer.
log%287%2Cx%29%2Blog%287%2Cy%29-log%287%2Cz%29 

The correct answer is

log%287%2C%28xy%2Fz%29%29

The properties of logarithms to use are

log%28b%2CA%29%2Blog%28b%2CC%29+=+log%28b%2CAC%29

log%28b%2CA%29-log%28b%2CC%29+=+log%28b%2C%28A%2FC%29%29

Arjun just doesn't understand the properties of logarithms.

Edwin