Page 1 of 2 12 LastLast
Results 1 to 10 of 11

Thread: Another Log Problem: logY^3 = logx(x+4)^2

  1. #1

    Another Log Problem: logY^3 = logx(x+4)^2

    Hello all

    I have another log problem which I was hoping someone could help me with.

    I have the following:-

    logY^3 = logx(x+4)^2

    I have been told that the above statement is the same as:-

    Y^3 = x(x+4)

    The bit I don't understand is where does the log go?
    What law allows the log to be removed from both sides?

    Can anyone help?

    Thank you.

    (assume base 10 log)

  2. #2
    Quote Originally Posted by Ted_Grendy View Post
    Hello all

    I have another log problem which I was hoping someone could help me with.

    I have the following:-

    logY^3 = logx(x+4)^2

    I have been told that the above statement is the same as:-

    Y^3 = x(x+4)^2

    The bit I don't understand is where does the log go?
    What law allows the log to be removed from both sides?

    Can anyone help?

    Thank you.

    (assume base 10 log)
    If log A = log B then A = B.
    Heavens to Murgatroyd!!

  3. #3
    Senior Member
    Join Date
    Dec 2014
    Posts
    2,477
    Quote Originally Posted by Ted_Grendy View Post
    Hello all

    I have another log problem which I was hoping someone could help me with.

    I have the following:-

    logY^3 = logx(x+4)^2

    I have been told that the above statement is the same as:-

    Y^3 = x(x+4)

    The bit I don't understand is where does the log go?
    What law allows the log to be removed from both sides?

    Can anyone help?

    Thank you.

    (assume base 10 log)
    It sounds so good, I'll repeat it again: If log A = log B, then A = B
    Last edited by Jomo; 12-05-2018 at 10:43 PM.
    A mathematician is a blind man in a dark room looking for a black cat which isnít there. - Charles R. Darwin

  4. #4
    Full Member
    Join Date
    Feb 2004
    Location
    Ottawa, Ontario
    Posts
    879
    If log(u) = log(v) then u = v
    I'm a man of few words...but I use 'em often!!

  5. #5
    Senior Member
    Join Date
    Dec 2014
    Posts
    2,477
    Quote Originally Posted by Denis View Post
    If log(u) = log(v) then u = v
    You have start off slow with some students and use A's and B's before U's and V's. Didn't they teach you nuttin in business school
    A mathematician is a blind man in a dark room looking for a black cat which isnít there. - Charles R. Darwin

  6. #6
    Full Member
    Join Date
    Feb 2004
    Location
    Ottawa, Ontario
    Posts
    879
    Quote Originally Posted by Jomo View Post
    Didn't they teach you nuttin in business school
    You forgot to end your sentence with a "?"
    Didn't they teach you nuttin in grammar school
    I'm a man of few words...but I use 'em often!!

  7. #7
    Senior Member
    Join Date
    Dec 2014
    Posts
    2,477
    Quote Originally Posted by Denis View Post
    You forgot to end your sentence with a "?"
    Didn't they teach you nuttin in grammar school
    I'm an American. So no, they did not teach me anything in grammar school.
    A mathematician is a blind man in a dark room looking for a black cat which isnít there. - Charles R. Darwin

  8. #8
    Full Member
    Join Date
    Feb 2004
    Location
    Ottawa, Ontario
    Posts
    879
    Quote Originally Posted by Jomo View Post
    I'm an American.
    ...and I'm Canadian .... that's because Canada had 1st pick!
    I'm a man of few words...but I use 'em often!!

  9. #9
    Senior Member
    Join Date
    Dec 2014
    Posts
    2,477
    Quote Originally Posted by Ted_Grendy View Post
    Hello all

    I have another log problem which I was hoping someone could help me with.

    I have the following:-

    logY^3 = logx(x+4)^2

    I have been told that the above statement is the same as:-

    Y^3 = x(x+4)

    The bit I don't understand is where does the log go?
    What law allows the log to be removed from both sides?

    Can anyone help?

    Thank you.

    (assume base 10 log)
    Log (for any base) is an increasing function which means that if A < B, then it must be that Log(A) < Log(B). So if A and B are different values it can't be that Log(A) = Log(B). But if Log(A) = Log(B), then yes A = B. In fact if A=B and they are both positive, then Log(A) = Log(B)

    Note: If you have something like Log(-2) = Log (x) we can NOT conclude that x=-2 because Log(-2) makes no sense (you can't take the log of 0 or a negative number).
    A mathematician is a blind man in a dark room looking for a black cat which isnít there. - Charles R. Darwin

  10. #10
    Quote Originally Posted by Jomo View Post
    It sounds so good, I'll repeat it again: If log A = log B, then A = B
    Jomo, If you "repeat it again" doesn't that mean that you are saying it for the nth time where n>=3 ?
    Heavens to Murgatroyd!!

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •