Results 1 to 6 of 6

Math Help - Trig Identities

  1. #1
    Newbie
    Joined
    Oct 2006
    Posts
    18

    Trig Identities

    Hi,
    I have my math exam in a few days and that's the last question I have to solve to complete the trig part.
    2sin x(1+cos x) = \frac {2sin^3 x} {1-cos x}
    I've been trying to use sin^2x + cos^2x for LS and RS however I'm getting nowhere with that, mainly because of the right side fraction.
    Any help appreciated.
    Thank you very much!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Math Engineering Student
    Krizalid's Avatar
    Joined
    Mar 2007
    From
    Santiago, Chile
    Posts
    3,654
    Thanks
    13
    2\sin x(1 + \cos x) = 2\sin x(1 + \cos x) \cdot \frac{{1 - \cos x}}<br />
{{1 - \cos x}} = \frac{{2\sin x\left( {1 - \cos ^2 x} \right)}}<br />
{{1 - \cos x}}.

    The rest follows.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Oct 2006
    Posts
    18
    I see...
    So you are allowed to multiply 1-cos x over 1-cos x at any time?
    I mean if I'd get anything similar in my exam I can just multiply it like that?
    Thanks
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Math Engineering Student
    Krizalid's Avatar
    Joined
    Mar 2007
    From
    Santiago, Chile
    Posts
    3,654
    Thanks
    13
    Quote Originally Posted by Universe View Post
    I see...
    So you are allowed to multiply 1-cos x over 1-cos x at any time?
    It's like multiplyin' by 1. It's like \frac aa.

    Quote Originally Posted by Universe View Post
    I mean if I'd get anything similar in my exam I can just multiply it like that?
    That depends of the problem.

    For example your trig. identity could've been tackled by workin' the RHS.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Eater of Worlds
    galactus's Avatar
    Joined
    Jul 2006
    From
    Chaneysville, PA
    Posts
    3,001
    Thanks
    1
    Work with the right side and show it equals the left side.

    Multiply top and bottom of right side by 1+cos(x)

    \frac{2sin^{3}(x)}{1-cos(x)}\cdot\frac{1+cos(x)}{1+cos(x)}

    =\frac{2sin^{3}(x)+2sin^{3}(x)cos(x)}{sin^{2}(x)}

    2sin(x)+2sin(x)cos(x)

    Factor:

    2sin(x)(1+cos(x))
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Newbie
    Joined
    Oct 2006
    Posts
    18
    Alright.
    Thank you very much guys.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Trig Identities
    Posted in the Calculus Forum
    Replies: 2
    Last Post: December 3rd 2009, 06:44 AM
  2. Trig identities
    Posted in the Trigonometry Forum
    Replies: 6
    Last Post: June 22nd 2009, 06:58 AM
  3. Trig Identities
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: November 9th 2008, 04:35 PM
  4. Trig Identities
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: November 7th 2008, 08:25 PM
  5. Trig Identities Help!!!!
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: April 14th 2008, 11:47 AM

Search Tags


/mathhelpforum @mathhelpforum