Results 1 to 5 of 5

Math Help - l'hospitals rule

  1. #1
    Junior Member
    Joined
    Mar 2010
    Posts
    35

    l'hospitals rule

    how does

    lim t*e^t
    t--> - infinity

    =

    lim t/e^-t
    t--> - infinity

    how does the e^t turn into e^-t in the denominator??

    THANKS
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Rhymes with Orange Chris L T521's Avatar
    Joined
    May 2008
    From
    Chicago, IL
    Posts
    2,844
    Thanks
    3
    Quote Originally Posted by calculus0 View Post
    how does

    lim t*e^t
    t--> - infinity

    =

    lim t/e^-t
    t--> - infinity

    how does the e^t turn into e^-t in the denominator??

    THANKS
    Its a rule of exponents: e^t=\frac{1}{e^{-t}}...
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Mar 2010
    Posts
    35
    is there an explanation or proof? or do i just have to memorize this.

    thank youu
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Rhymes with Orange Chris L T521's Avatar
    Joined
    May 2008
    From
    Chicago, IL
    Posts
    2,844
    Thanks
    3
    Quote Originally Posted by calculus0 View Post
    is there an explanation or proof? or do i just have to memorize this.

    thank youu
    You can think of it this way. Observe that e^te^{-t}=e^{t-t}=e^0=1. Thus, we see that either e^te^{-t}=1\implies e^{-t}=\frac{1}{e^t} or e^{t}=\frac{1}{e^{-t}}. In our case, we want the latter result.

    Does this clarify things a little bit?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Mar 2010
    Posts
    35
    OHH. ok. makes perfect sense!!

    thankss
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. l'hospitals rule help
    Posted in the Calculus Forum
    Replies: 8
    Last Post: November 16th 2009, 10:48 AM
  2. L'Hospitals rule and Mean Value Theorem
    Posted in the Calculus Forum
    Replies: 1
    Last Post: October 19th 2009, 08:41 PM
  3. L'hospitals rule
    Posted in the Calculus Forum
    Replies: 1
    Last Post: December 8th 2008, 03:21 PM
  4. L'Hospitals Rule
    Posted in the Calculus Forum
    Replies: 6
    Last Post: August 21st 2007, 03:05 PM
  5. l'hospitals rule
    Posted in the Calculus Forum
    Replies: 6
    Last Post: April 12th 2007, 10:52 PM

Search Tags


/mathhelpforum @mathhelpforum