Results 1 to 2 of 2

Math Help - Law of Cosines problem

  1. #1
    Member
    Joined
    May 2011
    Posts
    179
    Thanks
    6

    Law of Cosines problem

    Hi,

    I am asked to solve the triangle ABC with the given information:
    A=115 deg. b=46.8 c=51.3

    First I solved for side "a" and discovered it be to "82.8." Subsequent to this, I tried to find out what angle "B" was. Setting up the law of cosines equation (b^2=a^2+c^2-2acCosine B) and plugged in the values as follows:

    46.8^2=82.8^2+51.3^2-2(82.8)(51.3)Cos B

    Simplifying and dividing both sides of the equation, I acquire 2.21 and that was what cos B was equal to. To find that number in degrees, I clicked the cos inverse button and, to my dismay, received a prompt error message. I have tried this problem over and over. Where am I making this "foolish" mistake that I can not seem see?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    A Plied Mathematician
    Joined
    Jun 2010
    From
    CT, USA
    Posts
    6,318
    Thanks
    5
    Awards
    2
    Your a is correct. However, your 2.21 is incorrect. You're not correctly solving for cos(B). Try that again. You should get something between -1 and +1.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Law of cosines word problem
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: May 15th 2010, 09:17 PM
  2. Replies: 3
    Last Post: November 21st 2009, 06:51 AM
  3. Word problem has to do with law of cosines
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: October 7th 2008, 04:44 PM
  4. Law of Cosines
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: September 14th 2008, 07:53 AM
  5. Replies: 3
    Last Post: November 8th 2007, 11:39 AM

Search Tags


/mathhelpforum @mathhelpforum