SOLUTION: For some reason this question did not get posted the last time I asked, so I'm having to post it again. In this problem I've been asked to prove that loga x = c * logb x, where

Algebra ->  Exponential-and-logarithmic-functions -> SOLUTION: For some reason this question did not get posted the last time I asked, so I'm having to post it again. In this problem I've been asked to prove that loga x = c * logb x, where       Log On


   



Question 959994: For some reason this question did not get posted the last time I asked, so I'm having to post it again.
In this problem I've been asked to prove that loga x = c * logb x, where c is a constant. In other words, direct proportionality. I'd started out by representing the left side of the above equation with p and the right with q, then went (left side)/p = 1 and (right side)/q = 1, therefore (left side)/p = (right side)/q. I then cross-multiplied and used the division property of equality to get... exactly what I already had, (left side)/p = (right side)/q. Just when I thought I had it cracked too! A later problem has provided a clue - if c were equal to loga b, that might be very helpful, but I can't figure out how to get there without making that a given.
I'm completely stumped here. Help!

Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
This is not a statement to prove, unless you are allowed other important information: log%28a%2Cx%29=c%2Alog%28b%2Cx%29. This is a part of what you said, direct proportion or direct variation. The equation is true only because it is given as true.

Could you use Change of Base formula?
log%28a%2Cx%29=log%28b%2Cx%29%2Flog%28b%2Ca%29
-
log%28a%2Cx%29=log%28b%2Cx%29%2Flog%28b%2Ca%29=c%2Alog%28b%2Cx%29

%281%2Flog%28b%2Ca%29%29%2Alog%28b%2Cx%29=c%2Alog%28b%2Cx%29
If this is expected or given as true, then through their corresponding positions,
highlight_green%281%2Flog%28b%2Ca%29=c%29
Now then you have a statement about c, but not much is proved here about the given equation.