Page 2 of 2 FirstFirst 12
Results 16 to 20 of 20

Math Help - 3 Questions: 2 on Range and 1 on a logarithm

  1. #16
    Super Member
    Joined
    Oct 2006
    Posts
    679
    Awards
    1

    Re:

    Ok great thanks
    Follow Math Help Forum on Facebook and Google+

  2. #17
    Super Member
    Joined
    Oct 2006
    Posts
    679
    Awards
    1

    Re:

    What about the other problem on logs do you guys have any clue on that one?
    Follow Math Help Forum on Facebook and Google+

  3. #18
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    9,899
    Thanks
    327
    Awards
    1
    Quote Originally Posted by qbkr21 View Post

    3. When Log base b of A=2 and Log base b of D=5

    What is: Log base b of (a+d)
    log_bA = 2

    log_bD = 5

    I presume you want to know: log_b(A+D)? (Yes, case is important. A is not necessarily the same as a.)

    I couldn't tell you. With the given information I could tell you what log_b(AD) is (its 2 + 5 = 7).

    Let me show you why this is so hard.

    log_bA = 2 means that b^2 = A. Similarly log_bD = 5 means b^5 = D. So
    A + D = b^2 + b^5

    But this is NOT a simple power of b. There IS an exponent c such that b^c = b^2 + b^5, but this is not an easy equation to solve for a general value of b, if it's even possible to do generally. (However if we know the value of b we can numerically estimate it.)

    If it still seems simple, try to find c for 2^c = 2^2 + 2^5 = 4 + 32 = 36. So c = log_236 \approx 5.169925001. But if b = 3, then c = log_2252 \approx 5.033103256.

    -Dan
    Follow Math Help Forum on Facebook and Google+

  4. #19
    Global Moderator

    Joined
    Nov 2005
    From
    New York City
    Posts
    10,616
    Thanks
    9
    I think he wants to know,
    \log_b (A\cdot D)
    Not, \log_b(A+B)
    It seems that either he copied wrong of his teacher posed an unfair problem.
    Follow Math Help Forum on Facebook and Google+

  5. #20
    Super Member
    Joined
    Oct 2006
    Posts
    679
    Awards
    1

    Re:

    Dan you are right I did A time D and got 15 and that was wrong on the test. Maybe I am in way over my head, I might should have just added them. But when you expand logs through mulitiplication you add them, this is what I thought but as stated she marked it wrong. My teacher obviously wanted something totally different. Thanks Guys.
    Follow Math Help Forum on Facebook and Google+

Page 2 of 2 FirstFirst 12

Similar Math Help Forum Discussions

  1. Logarithm questions
    Posted in the Algebra Forum
    Replies: 4
    Last Post: March 9th 2009, 01:42 AM
  2. Logarithm questions
    Posted in the Algebra Forum
    Replies: 1
    Last Post: January 12th 2009, 03:51 PM
  3. Logarithm questions
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: June 23rd 2007, 08:28 PM
  4. some simple logarithm questions
    Posted in the Algebra Forum
    Replies: 1
    Last Post: May 19th 2007, 06:24 AM
  5. Some Logarithm Questions
    Posted in the Algebra Forum
    Replies: 8
    Last Post: December 21st 2006, 11:48 AM

Search Tags


/mathhelpforum @mathhelpforum