Results 1 to 3 of 3

Math Help - Angle in a tetrahedron

  1. #1
    Senior Member Mukilab's Avatar
    Joined
    Nov 2009
    Posts
    468

    Angle in a tetrahedron

    The diagram (sorry, had a bug with photoshop) shows a tetrahedron
    AD is perpendicular to both AB and AC

    AB=10cm
    AC=8cm
    AD=5cm
    Angle BAC = 90 degrees

    Find the size of angle BDC

    Please could someone help me out through this step by step? I know what to do to get the answer just not how to do it.

    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 Mukilab View Post
    The diagram (sorry, had a bug with photoshop) shows a tetrahedron
    AD is perpendicular to both AB and AC

    AB=10cm
    AC=8cm
    AD=5cm
    Angle BAC = 90 degrees

    Find the size of angle BDC

    Please could someone help me out through this step by step? I know what to do to get the answer just not how to do it.
    1. Use the 3 right triangles to calculate the lengths of the triangle BDC.
    Spoiler:
    \sqrt{89}, \sqrt{125}, \sqrt{164}


    2. Use the Cosine rule to calculate the angle \angle(BDC)
    Spoiler:
    I've got \angle(BDC) \approx 76.29^\circ
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Senior Member Mukilab's Avatar
    Joined
    Nov 2009
    Posts
    468
    I had the three lengths, just didn't know the cosine law. Thanks
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Tetrahedron
    Posted in the Geometry Forum
    Replies: 6
    Last Post: October 2nd 2012, 03:00 PM
  2. tetrahedron,
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: July 14th 2009, 02:09 AM
  3. Find the angle in a Tetrahedron
    Posted in the Geometry Forum
    Replies: 3
    Last Post: April 26th 2009, 08:35 AM
  4. tetrahedron
    Posted in the Geometry Forum
    Replies: 1
    Last Post: January 8th 2009, 01:35 PM
  5. Tetrahedron
    Posted in the Geometry Forum
    Replies: 4
    Last Post: March 21st 2008, 02:07 AM

Search Tags


/mathhelpforum @mathhelpforum