Results 1 to 4 of 4

Math Help - Identity help.

  1. #1
    Member wiseguy's Avatar
    Joined
    Jul 2010
    Posts
    101

    Identity help.

    I am ABSOLUTLY stuck on this idenity problem! Anyone please help!


    Prove algebraically that the equation is an identity:

    (5cosC-2sinC)^2+(2cosC+5sinC)^2=29



    Please help! Thank you so much!
    Last edited by mr fantastic; July 15th 2010 at 05:08 PM. Reason: Removed excessive !'s from title, removed quote tags from question, removed excessive emoticons.
    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
    I would probably multiply it out, and use \sin^{2}(C)+\cos^{2}(C)=1 a few times.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    A riddle wrapped in an enigma
    masters's Avatar
    Joined
    Jan 2008
    From
    Big Stone Gap, Virginia
    Posts
    2,551
    Thanks
    12
    Awards
    1
    Quote Originally Posted by wiseguy View Post
    I am ABSOLUTLY stuck on this idenity problem! Anyone please help!





    Please help! Thank you so much!
    Hi wiseguy,

    (5 \cos C - 2 \sin C)^2+(2 \cos C+5 \sin C)^2=29

    25\cos^2 C-20 \cos C \sin C+4 \sin^2 C + (4\cos^2 C+20 \cos C \sin C+ 25 \sin^2 C)=29

    29 \cos^2 C+29 \sin^2 C=29

    29(\cos^2 C+\sin^2 C)=29

    29(1)=29

    29=29
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Member wiseguy's Avatar
    Joined
    Jul 2010
    Posts
    101
    Thank you!! Duh to me! alskjd;f
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. identity
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: December 13th 2009, 03:09 PM
  2. identity 2
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: July 28th 2009, 12:26 AM
  3. identity
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: January 21st 2009, 10:40 PM
  4. Sin/Cos Identity
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: September 1st 2008, 05:41 PM
  5. Identity
    Posted in the Algebra Forum
    Replies: 1
    Last Post: February 24th 2008, 12:10 PM

Search Tags


/mathhelpforum @mathhelpforum