Maths help (Natural Logarithms)

DRZ · 1 Sep 2006 at 22:14

Doing some maths and I have tied my brain in a knot. I know its simple but I doubted myself and now I need help.

All I need to do is simplify:

(ln(x^2)+ln(xy)-ln(y))/3 (all the logs over three)

Now, I seem to have simplified it to just ln(x) but it doesnt "feel" right and I just cant get my head into gear over it.

Help please!

Chris1712 · 1 Sep 2006 at 22:15

The answer is 42.

MastermindUK · 1 Sep 2006 at 22:28

I haven't maths in a while but I think you're right with ln(x), if I'm remembering my log rules right.

Edit: I think it might be wrong now actually... can't make my mind up.

DRZ · 1 Sep 2006 at 22:41

Well, I arrived at ln(x) like this:

ln(xy) - ln(y) = ln(xy/y) (using an identity there) leaving you with ln(x).

ln(x^2) + ln(x) = ln(x^3)

ln(x^3) = 3ln(x)

3ln(x)/3 = ln(x)

Correct?

beh · 1 Sep 2006 at 22:55

I'm pretty sure thats right. Cept for the typo "ln(xy) - ln(x) = ln(xy/y)", you obviously meant "ln(xy) - ln(y) = ln(xy/y)".

DRZ · 1 Sep 2006 at 23:18

beh said:
I'm pretty sure thats right. Cept for the typo "ln(xy) - ln(x) = ln(xy/y)", you obviously meant "ln(xy) - ln(y) = ln(xy/y)".

Yes I did, whoops! Thanks for pointing it out and thanks for helping out

Flanders · 1 Sep 2006 at 23:21

Laws of Logs:

1. ln(a) + ln(b) = ln(ab)
2. ln(a) - ln(b) = ln(a/b)
3. ln(a³) = 3ln(a)

For clarification, this is all you need for this question

Chris1712 said:
The answer is 42.

Thanks a bunch for your contribution, Im sure the thread starter really appreciated your input.

DRZ · 1 Sep 2006 at 23:32

Flanders said:
Laws of Logs:

1. ln(a) + ln(b) = ln(ab)
2. ln(a) - ln(b) = ln(a/b)
3. ln(a³) = 3ln(a)

For clarification, this is all you need for this question

Thanks a bunch for your contribution, Im sure the thread starter really appreciated your input.

Cheers.

As for that wonderful post - the ignore list is all you need for people like that