# The scope/limitation of logab X

• November 23rd 2009, 04:25 PM
Bzaher
The scope/limitation of logab X
loga X = C and logb X = D
i got it up to log ab X = (cd)/(c+d)
the question asked what the scope and/or limitations are. I know that ab and X can't be negatives but i dont know the rest
• November 24th 2009, 03:12 AM
stapel
I'm sorry, but I'm not clear on what you're being asked to do...? (Wondering)

Please reply with the full and exact text of the exercise, and the complete instructions. Thank you! (Wink)
• November 24th 2009, 03:22 AM
HallsofIvy
Quote:

Originally Posted by Bzaher
loga X = C and logb X = D
i got it up to log ab X = (cd)/(c+d)
the question asked what the scope and/or limitations are. I know that ab and X can't be negatives but i dont know the rest

I presume you are asking about restrictions on the base of a logarithm and the domain. "not negative" is not enough. They also cannot be zero. ab and X must be positive.
• November 24th 2009, 04:12 AM
Soroban
Hello, Bzaher!

Quote:

$\log_a X \,=\, c,\;\;\log_b X \,=\, d$

i got it up to: . $\log_{ab} X \:=\:\frac{cd}{c+d}$

The question asked what the scope and/or limitations are.

The scope and limitations of what?

Here are the restrictions: . $\begin{Bmatrix}X \:>\:0 \\
a \,>\,0,\;a\,\neq\,1 \\ b\,>\,0,\;b\,\neq\,1 \\ c+d\,\neq\,0\end{Bmatrix}$