Results 1 to 6 of 6

Math Help - area of a triangle with vertices

  1. #1
    Super Member
    Joined
    Oct 2008
    From
    Bristol, England
    Posts
    897

    area of a triangle with vertices

    hi,

    i need to prove that the triangle with vertices (-2,8), (3,20) and (11,8) is isoceles. Find its area.

    now for this question would i just need to draw it on a graph and dop;
    BxH/2
    13x12=156/2=78

    if this is correct so far im unsure what to do after this point to find that it is isoceles.
    help is required please!

    thanks!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,605
    Thanks
    1573
    Awards
    1

    Re: area of a triangle with vertices

    Quote Originally Posted by andyboy179 View Post
    i need to prove that the triangle with vertices (-2,8), (3,20) and (11,8) is isoceles. Find its area.
    You can find the length of each side.
    The use the semi-perimeter rule to find the area.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member
    Joined
    Oct 2008
    From
    Bristol, England
    Posts
    897

    Re: area of a triangle with vertices

    i don't know what the semi-perimeter rule is.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,663
    Thanks
    603

    Re: area of a triangle with vertices

    Hello, andyboy179!

    Prove that the triangle with vertices A(-2,8), B(3,20) and C(11,8) is isoceles.
    Find its area.


    For this question, would i just need to draw it on a graph and do:

    . . \text{Area} \:=\:\tfrac{1}{2}bh \:=\:\tfrac{1}{2}(13)(12) \:=\:78\;? . . . . Yes!

    If this is correct so far, I;m unsure what to do after this point to find that it is isoceles.

    Excellent work!
    We see that AC is horizontal and AC = 13.
    And we find that the altitude from B is 12.

    An isosceles triangle has two equal sides.
    Use the Distance Formula on side AB.
    . . You'll find that it too is 13 units long.

    (We also find that BC is not 13 units long.
    Hence, the triangle is not equilateral.)

    Follow Math Help Forum on Facebook and Google+

  5. #5
    Super Member
    Joined
    Oct 2008
    From
    Bristol, England
    Posts
    897

    Re: area of a triangle with vertices

    Quote Originally Posted by Soroban View Post
    Hello, andyboy179!


    Excellent work!
    We see that AC is horizontal and AC = 13.
    And we find that the altitude from B is 12.

    An isosceles triangle has two equal sides.
    Use the Distance Formula on side AB.
    . . You'll find that it too is 13 units long.

    (We also find that BC is not 13 units long.
    Hence, the triangle is not equilateral.)

    hi, how do i use the distace formula on side AB?
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Super Member
    Joined
    Oct 2008
    From
    Bristol, England
    Posts
    897

    Re: area of a triangle with vertices

    sorry i know how to do it!!! mental block!! thanks alot for the answer!!!!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Area of a triangle given the vertices.
    Posted in the Geometry Forum
    Replies: 2
    Last Post: March 25th 2010, 07:13 PM
  2. Replies: 4
    Last Post: March 16th 2010, 07:04 PM
  3. [SOLVED] Area of right triangle with 3 vertices
    Posted in the Advanced Algebra Forum
    Replies: 2
    Last Post: March 6th 2010, 05:04 AM
  4. Replies: 8
    Last Post: September 5th 2009, 03:01 PM
  5. triangle vertices
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: March 7th 2007, 04:49 AM

Search Tags


/mathhelpforum @mathhelpforum