Results 1 to 3 of 3

Math Help - Find cos(A - B) and cos(A) - cos(B) given A+B=60 and CosA + Cos B=1

  1. #1
    Newbie
    Joined
    Jul 2011
    Posts
    11

    Find cos(A - B) and cos(A) - cos(B) given A+B=60 and CosA + Cos B=1

    A+B=60degrees and CosA + Cos B=1 ....find
    1) cos(A-B)
    2)cosA - Cos B
    Last edited by mr fantastic; July 11th 2011 at 03:38 PM. Reason: Re-titled
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor Siron's Avatar
    Joined
    Jul 2011
    From
    Norway
    Posts
    1,250
    Thanks
    20

    Re: trignometry --problem plz help

    You have: A+B=60 and cos(A)+cos(B)=1
    If you write:
    cos(A)+cos(B)=1 as 2cos((A+B)/2).cos((A-B)/2)=1
    You can solve this one because you know A+B=60 so (A+B)/2=30
    You have now: 2cos(30).cos((A-B)/2)=1

    Now try to finish it.
    Last edited by Siron; July 12th 2011 at 03:20 AM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    May 2011
    From
    Islamabad
    Posts
    96
    Thanks
    1

    Re: trignometry --problem plz help

    from given cosA = cos(60-B) substituting in 2nd and simplifying


    we get cos(B-30) = 1/(sqrt3) gives B = 84.73561
    now you can find A and required values
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 8
    Last Post: March 22nd 2011, 04:57 PM
  2. Replies: 2
    Last Post: July 5th 2010, 08:48 PM
  3. sina*cosa=4/7 , a=?
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: February 2nd 2010, 10:50 PM
  4. 8*cosA*cosB*CosC
    Posted in the Trigonometry Forum
    Replies: 7
    Last Post: October 7th 2009, 12:44 AM
  5. Replies: 2
    Last Post: April 17th 2008, 09:51 AM

Search Tags


/mathhelpforum @mathhelpforum