Results 1 to 7 of 7

Math Help - Finding angles in a triangle.

  1. #1
    Newbie s2951's Avatar
    Joined
    Nov 2009
    From
    LaLaLAND :D
    Posts
    13

    Question Finding angles in a triangle.

    a=5m , b=8m , c=7m

    a^2= b^2+c^2-2bc Cos A
    (5)^2= (8)^2+(7)^2-2(8)(7) Cos A
    Cos A= 5^2-8^2+7^2/-2(8)(7)
    Cos A= 10/-112
    Angle A= -0.0898
    Angle A= 95 Degrees 9 minutes

    How to find other B & C angle?

    This is what i work out but stuck.........

    a/Sin A = b/SinB
    5/Sin 95 Degrees 9 minutes = 8/Sin B
    Sin B = (8)(Sin 95 Degrees 9 minutes)/5
    Sin B = 1.5939

    Problem is i calculate using sin^-1...

    Thanks much
    Last edited by mr fantastic; February 5th 2010 at 12:21 PM. Reason: Changed post title
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Newbie
    Joined
    Feb 2010
    From
    Fairfield, Ca
    Posts
    21
    the same way?

    b^2= a^2+c^2-2ac Cos B
    c^2= b^2+a^2-2ba Cos C

    you got angle A wrong too, check your calculations
    Cos A= (5^2-8^2-7^2)/(-2(8)(7))
    Last edited by Solarmew; February 5th 2010 at 04:20 AM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie s2951's Avatar
    Joined
    Nov 2009
    From
    LaLaLAND :D
    Posts
    13
    Quote Originally Posted by Solarmew View Post
    the same way?
    u mean now need to calculate using Cos B using cosine rule?

    SOLVED. THX
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie s2951's Avatar
    Joined
    Nov 2009
    From
    LaLaLAND :D
    Posts
    13
    Quote Originally Posted by Solarmew View Post
    the same way?

    b^2= a^2+c^2-2ac Cos B
    c^2= b^2+a^2-2ba Cos C

    you got angle A wrong too
    which part?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Feb 2010
    From
    Fairfield, Ca
    Posts
    21
    either cosine or sine law would've worked :]
    good job
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Newbie
    Joined
    Feb 2010
    From
    Fairfield, Ca
    Posts
    21
    minus 7 not plus :] and dun forget the order of operations
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Newbie s2951's Avatar
    Joined
    Nov 2009
    From
    LaLaLAND :D
    Posts
    13
    Quote Originally Posted by Solarmew View Post
    minus 7 not plus :] and dun forget the order of operations
    Noted.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: March 29th 2011, 04:58 AM
  2. Replies: 4
    Last Post: August 6th 2010, 10:25 PM
  3. Finding angles in a triangle and a circle.
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: February 4th 2010, 05:13 PM
  4. Finding angles in a right triangle
    Posted in the Geometry Forum
    Replies: 5
    Last Post: September 13th 2008, 07:44 AM
  5. angles with triangle
    Posted in the Geometry Forum
    Replies: 1
    Last Post: October 18th 2007, 06:54 PM

Search Tags


/mathhelpforum @mathhelpforum