Results 1 to 4 of 4

Math Help - Circles and co-ordinates

  1. #1
    Junior Member
    Joined
    Oct 2007
    Posts
    37

    Circles and co-ordinates

    Hey

    Prove that the line y=2x is a tangent to the circle x^2 + y^2 - 8x -y +5=0
    and find the coordinates of the point of contact.

    Can somebody please help, I am just really confused with what to do and where to start.

    THANKS
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Newbie
    Joined
    Dec 2007
    Posts
    11
    First, find out where the line and circle intersect. It should be a single point. Next, prove that a second line going from the center of the circle to the intersection point is perpendicular to the line y=2x. That is a non-calculus method, which I'm assuming is your desired approach.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Oct 2007
    Posts
    37

    Smile Thanks

    Thanks, that's brilliant.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    10,117
    Thanks
    382
    Awards
    1
    Quote Originally Posted by mathdeity View Post
    First, find out where the line and circle intersect. It should be a single point. Next, prove that a second line going from the center of the circle to the intersection point is perpendicular to the line y=2x. That is a non-calculus method, which I'm assuming is your desired approach.
    Actually, for the case of a circle, intersection at one point is sufficient to guarantee that the line is a tangent.

    -Dan
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Prove that every rigid motion transforms circles into circles
    Posted in the Differential Geometry Forum
    Replies: 4
    Last Post: February 11th 2010, 06:00 PM
  2. Co-ordinates
    Posted in the Geometry Forum
    Replies: 1
    Last Post: December 29th 2009, 05:42 AM
  3. Replies: 2
    Last Post: October 6th 2009, 08:04 AM
  4. co-ordinates
    Posted in the Algebra Forum
    Replies: 2
    Last Post: April 3rd 2009, 03:36 PM
  5. Co-ordinates
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: March 16th 2006, 05:08 AM

Search Tags


/mathhelpforum @mathhelpforum