x Turn on thread page Beta
 You are Here: Home >< Maths

# c2 Logs problem. watch

1. 2log3x-log3 7x = 1

I re-arrange first log as Log3x^2

so Log3 x^2 - log3 7x = 1

Using division rule, Log3 x^2/7x = 1

I don't know what to do after this?
2. Is that log base 3?
3. What you have is equivalent to an exponential equation:

x^2/7x = 3^1 = 3
4. therefore 3 to the power 1 = x^2/7x

therefore 3 = x^2/7x

therefore 21x = x^2

that is if i am interpreting your question correctly...
hope it helps
5. (Original post by Ben121)
Is that log base 3?
yeah
6. (Original post by Extricated)
2log3x-log3 7x = 1

I re-arrange first log as Log3x^2

so Log3 x^2 - log3 7x = 1

Using division rule, Log3 x^2/7x = 1

I don't know what to do after this?

As it equals 1, x^2/7x must equal 3.

as Log3 3=1

x^2/7x = 3
x^2 = 21x
x^2 - 21x = 0

and solve.

x(x-21)=0

x=0 or x-21=0
x=21

Hope that helps, if anything needs explaining just ask. I'm revising this right now, I have a NAB tomorrow (what they call unit tests in Scotland).
7. i think if you put the whole thing in log base 3 then it becomes easier. So 1 becomes log3 3 then go from there.

so x^2 -21x = 0

x(x-21)=0
8. I have solved it thanks to all your help! thanks very much!
9. ive made a quick video for you on my blog which can be found in the signature. Hope that helps.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 28, 2011
Today on TSR

### I've studied the wrong subject

...Should I go back to school?

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams