Solving equations with logs: log (2x + 5) * log (9x^2) = 0  TOPIC_SOLVED

Quadratic equations and inequalities, variation equations, function notation, systems of equations, etc.

Solving equations with logs: log (2x + 5) * log (9x^2) = 0

Postby santaclaus on Fri Apr 10, 2009 9:59 pm

how do I go about solving?

log (2x+5) x log (9x2)=0

I would start by distributing log to 2x and then log 5? and then go from there?
santaclaus
 
Posts: 41
Joined: Tue Mar 03, 2009 12:17 am

Sponsor

Sponsor
 

Re: Solving equations with logs

Postby Martingale on Fri Apr 10, 2009 11:07 pm

santaclaus wrote:how do I go about solving?

log (2x+5) x log (9x2)=0

I would start by distributing log to 2x and then log 5? and then go from there?


if the problem is

then you need

or

so or

since
User avatar
Martingale
 
Posts: 363
Joined: Mon Mar 30, 2009 1:30 pm
Location: USA

Re: Solving equations with logs: log (2x + 5) * log (9x^2) = 0

Postby santaclaus on Mon Apr 13, 2009 6:58 am

how do you know that log 2x+5=1? where you wrote the answer? Is it true that log A * log B = log A + log B =0? I'm not sure where you're getting 2 equations =1?
santaclaus
 
Posts: 41
Joined: Tue Mar 03, 2009 12:17 am

  TOPIC_SOLVED

Postby stapel_eliz on Mon Apr 13, 2009 11:01 am

santaclaus wrote:how do you know that log 2x+5=1?

You don't. You know (by factoring, like you learned back when you were studying quadratic equations), that log(2x + 5) = 0. By using what you know about logs, you then converted this log equation into its equivalent exponential equation. :wink:
User avatar
stapel_eliz
 
Posts: 1784
Joined: Mon Dec 08, 2008 4:22 pm

Re: Solving equations with logs: log (2x + 5) * log (9x^2) = 0

Postby Martingale on Mon Apr 13, 2009 10:31 pm

santaclaus wrote:how do you know that log 2x+5=1? where you wrote the answer? Is it true that log A * log B = log A + log B =0? I'm not sure where you're getting 2 equations =1?




so
User avatar
Martingale
 
Posts: 363
Joined: Mon Mar 30, 2009 1:30 pm
Location: USA


Return to Intermediate Algebra

cron