Math Is Fun Forum

sachik

Member

Registered: 2008-02-28

Posts: 9

Logarithms

how would you solve

log(2x+2) + log x - log(12)=0

and

log½ gives the same answer as -log2

true or false?

explain why?

any help would be much appreciated!!!

Last edited by sachik (2008-05-17 20:03:10)

Kurre

Member

Registered: 2006-07-18

Posts: 280

Re: Logarithms

In both questions, use that logx+logy=logxy, logx-logy=log(x/y)

Identity

Member

Registered: 2007-04-18

Posts: 934

Re: Logarithms

Using the rules:

You get:

Using

,

or

BUT! x cannot equal -3, because if you plug -3 back into the equation, you will get the log of a negative number. You cannot have the log of a negative number, so x = 2 is the only solution.

For your second question,

But

(anything to the power of 0 is 1)

Last edited by Identity (2008-05-17 20:51:11)

sachik

Member

Registered: 2008-02-28

Posts: 9

Re: Logarithms

Thanks a lot, everything makes better sense now