Results 1 to 3 of 3

Math Help - logarithms

  1. #1
    Junior Member
    Joined
    Nov 2007
    Posts
    41

    logarithms

    I think this is supposed to go here...anyways..

    I need help with this log.

    Solve for x
    5^(2x) - 5^(x) - 20 = 0

    please and thank you...I've been stuck on it for a half hour now.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    earboth's Avatar
    Joined
    Jan 2006
    From
    Germany
    Posts
    5,807
    Thanks
    116
    Quote Originally Posted by CenturionMonkey View Post
    I think this is supposed to go here...anyways..

    I need help with this log.

    Solve for x
    5^(2x) - 5^(x) - 20 = 0

    please and thank you...I've been stuck on it for a half hour now.
    Hello,

    use the substitution y = 5^x and your equation becomes:
    5^{2x} - 5^x - 20 = 0~\longrightarrow~y^2-y-20=0

    This is a quadratic equation in y. Solve for y and don't forget to re-substitute to calculate x. I've got x = 1
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Nov 2007
    Posts
    41
    ahh I see. Thanks a lot, yep the answer sheet says it's 1.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. logarithms help
    Posted in the Algebra Forum
    Replies: 4
    Last Post: April 6th 2010, 06:29 PM
  2. Logarithms
    Posted in the Algebra Forum
    Replies: 2
    Last Post: April 6th 2010, 04:46 PM
  3. logarithms
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: March 24th 2010, 04:26 AM
  4. Logarithms
    Posted in the Algebra Forum
    Replies: 3
    Last Post: March 18th 2010, 02:52 PM
  5. logarithms
    Posted in the Algebra Forum
    Replies: 4
    Last Post: April 16th 2008, 09:55 AM

Search Tags


/mathhelpforum @mathhelpforum