Results 1 to 2 of 2

Math Help - Finding the equation of a derivative line wihtout knowing coordinates

  1. #1
    Newbie
    Joined
    Jan 2011
    Posts
    6

    Finding the equation of a derivative line wihtout knowing coordinates



    I haven't figured out how to type equations on here... I'll have to withhold the numbers till I figure it out.

    Anyway, you know the equation of the ellipse and the coordinates of point Q. You have to find the equation of the line.

    Finding the derivative is easy enough, but I'm not sure where to go from there....
    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
    Quote Originally Posted by iflyboats View Post

    I haven't figured out how to type equations on here... I'll have to withhold the numbers till I figure it out.

    Anyway, you know the equation of the ellipse and the coordinates of point Q. You have to find the equation of the line.

    Finding the derivative is easy enough, but I'm not sure where to go from there....
    If I understand your question correctly you are looking for the equation of the tangent line which passes through Q(q, 0) and has P as the tangent point.

    If so:

    1. All lines passing through Q have the equation: y = m (x -q)

    2. Determine the Points of intersection between the line and the ellipse:

    x^2/a^2 + (m(x-q))^2/b^2 = 1

    DSolve for x.

    3. To get a tangent point the discriminant must be zero. And this is the additional condition to find the tangent line.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: January 10th 2011, 07:19 AM
  2. Replies: 6
    Last Post: October 10th 2010, 11:51 AM
  3. Replies: 6
    Last Post: July 23rd 2010, 12:36 PM
  4. Replies: 2
    Last Post: June 8th 2010, 04:59 PM
  5. Replies: 7
    Last Post: October 22nd 2007, 08:01 PM

Search Tags


/mathhelpforum @mathhelpforum