Results 1 to 7 of 7

Math Help - Equation of tangent line

  1. #1
    Junior Member
    Joined
    Nov 2010
    Posts
    57

    Equation of tangent line

    Find equation of line tangent to the hyperbola \frac{2}{x} at the point (4,1/2)

    I can't see where the y-intercept comes from... f' = -2x^{-2} \Rightarrow f'(4) = -\frac{1}{8} so the equation is y = -\frac{1}{8}x + ?

    I don't where to go from finding the slope, do I just keep plugging in points for f'(x)?????
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    earboth's Avatar
    Joined
    Jan 2006
    From
    Germany
    Posts
    5,830
    Thanks
    123

    Re: Equation of tangent line

    Quote Originally Posted by Foxlion View Post
    Find equation of line tangent to the hyperbola \frac{2}{x} at the point (4,1/2)

    I can't see where the y-intercept comes from... f' = -2x^{-2} \Rightarrow f'(4) = -\frac{1}{8} so the equation is y = -\frac{1}{8}x + ?

    I don't where to go from finding the slope, do I just keep plugging in points for f'(x)?????
    You have the coordinates of the tangent point and the slope of the tangent line. Use slope-point-equation of a straight line:

    y-\frac12 = -\frac18(x-4)~\implies~\boxed{y = -\frac18x+1}
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Sep 2010
    Posts
    185
    Thanks
    13

    Re: Equation of tangent line

    y=-\frac{1}{8}x+l and l can be found using the condition that the point \left(4,\frac{1}{2}\right) belongs to that tangent line. Use the coordinates of that point instead of x and y in and you will get l.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Member
    Joined
    Sep 2010
    Posts
    185
    Thanks
    13

    Re: Equation of tangent line

    Earboth beat me to it.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Nov 2010
    Posts
    57

    Re: Equation of tangent line

    Quote Originally Posted by Foxlion View Post
    y = -\frac{1}{8}x + ?
    never mind
    Follow Math Help Forum on Facebook and Google+

  6. #6
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,993
    Thanks
    1656

    Re: Equation of tangent line

    Are you saying that earboth and mathoman were just wasting their time responding to your post?
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Junior Member
    Joined
    Nov 2010
    Posts
    57

    Re: Equation of tangent line

    Quote Originally Posted by HallsofIvy View Post
    Are you saying that earboth and mathoman were just wasting their time responding to your post?
    no, I posted that before seeing their replies. I looked at what I had posted and saw that I simply had to plug in an x and a y and solve for the ?
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 6
    Last Post: January 12th 2011, 02:38 PM
  2. Equation of the Tangent Line
    Posted in the Calculus Forum
    Replies: 3
    Last Post: October 21st 2010, 09:10 PM
  3. equation for tangent line
    Posted in the Calculus Forum
    Replies: 2
    Last Post: January 5th 2009, 09:51 AM
  4. Equation of tangent line.
    Posted in the Calculus Forum
    Replies: 2
    Last Post: April 3rd 2008, 08:17 AM
  5. equation of the tangent line
    Posted in the Calculus Forum
    Replies: 3
    Last Post: October 16th 2007, 01:47 PM

Search Tags


/mathhelpforum @mathhelpforum