basic logarithm problem

Quote:

Originally Posted by cbbplanet

Hi, I just don't get this sort of Logarithm problems that have same two variable in the equation.
The problem is:
Solve for x
log x + log(x+3)=1

thanks for the help =]

Rewrite using log properties

$Log(x(x+3))=1$

rewrite in expo form.

$x(x+3)=10 \iff x^2+3x-10=0$

$(x-2)(x+5)=0$

So x=2 or x=-5

But if you plug x=-5 into the original equation you end up with the log(-5)

which is undefined. So the only solution is x=2.