Results 1 to 3 of 3

Math Help - tangent

  1. #1
    Member
    Joined
    Aug 2009
    Posts
    211

    tangent

    hi, could someone show me the steps to answering this question please?

    show that the lengths of the tangents from the point (h, k) to the circle x^2 + y^2 + 2fx + 2gy + c = 0 are \sqrt {h^2 + k^2 + 2fh + 2gk + c}

    thanks, Mark
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member pacman's Avatar
    Joined
    Jul 2009
    Posts
    448
    show that the lengths of the tangents from the point to the circle are

    -------------------------------------------------------------------------------------------------------------------------------------------------------

    equation of a circle: (x + f)^2 + (y + g)^2 = 2 - c = (sqrt(2 - c))^2.

    a line tangent to circle forms a right triangle, where the point of tangency as the right angle, one point at the center of a circle (-f,-g) and the other at a certain point (h,k.)

    use distance formula . . . .
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Aug 2009
    Posts
    211
    hi, i sort of see where you're going with that. but wouldn't there be a left over or something that you'd have to minus after you put the equation into brackets ie f^2 and g^2 in

    (x + f)^2 - f^2 + (y + g)^2 - g^2 = - c
    \implies (x + f)^2 + (y + g)^2 = - c + g^2 + f^2

    or is that wrong?
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 1
    Last Post: September 27th 2011, 12:17 PM
  2. Replies: 6
    Last Post: January 12th 2011, 02:38 PM
  3. Replies: 6
    Last Post: April 7th 2010, 02:34 PM
  4. Tangent
    Posted in the Calculus Forum
    Replies: 3
    Last Post: March 8th 2010, 04:42 AM
  5. Replies: 3
    Last Post: February 20th 2009, 05:28 AM

Search Tags


/mathhelpforum @mathhelpforum