# logarithm equation help.

• Feb 10th 2013, 04:59 AM
agehayoshina
logarithm equation help.
the equations in question are log4(x+1)-log43=1 and 4(7x)-72x=3

not sure what method to use to approach these.

thanks

age
• Feb 10th 2013, 05:21 AM
Plato
Re: logarithm equation help.
Quote:

Originally Posted by agehayoshina
the equations in question are $\log_4(x+1)-\log_4(3)=1$ and $4(7^x)-7^{2x}=3$
not sure what method to use to approach these.

The first one is $\frac{x+1}{3}=4$.

The second is equivalent to $u^2-4u+3=0$ where $u=7^x$.
• Feb 10th 2013, 05:37 AM
agehayoshina
Re: logarithm equation help.
In the first problem Plato used the fact that $log a- log b= log(a/b)$ and that $log_b(b)= 1$.
For the second, he substituted y for $7^x$, as he said, and used the fact that $7^{2x}= (7^x)^2= y^2$.