Results 1 to 5 of 5

Math Help - Find sin(2A) if A is an acute angle with cos A = 1/3. Please help!!

  1. #1
    Newbie
    Joined
    Dec 2008
    Posts
    3

    Find sin(2A) if A is an acute angle with cos A = 1/3. Please help!!

    I'm stuck. All help is greatly appreciated.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member 11rdc11's Avatar
    Joined
    Jul 2007
    From
    New Orleans
    Posts
    894
    Ok since the problem stated that cos is a acute angle that means you in the 1st quad so your sin is going to be positive as well.

    Now use pyth to figure out what sin A is

    y^2 + 1^2 = 3^2

    y^2 = 8

    y = 2\sqrt{2}

    so

    \sin {A} = \frac{2\sqrt{2}}{3}

    Now

    \sin{2A} = 2\sin{A}\cos{A}

    Can you finish up
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Dec 2008
    Posts
    3
    Thanks very much. I'll see what I can do.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Dec 2008
    Posts
    3
    Does it work out to:

    4(square root 2)/9 ?

    Follow Math Help Forum on Facebook and Google+

  5. #5
    Super Member 11rdc11's Avatar
    Joined
    Jul 2007
    From
    New Orleans
    Posts
    894
    Quote Originally Posted by right-as-rain View Post
    Does it work out to:

    4(square root 2)/9 ?


    You tell me

    2\sin{A}\sin{A}

    and knowing

    \sin {A} = \frac{2\sqrt{2}}{3}

    \cos {A} = \frac{1}{3}

    so just plug in

    \bigg(2\bigg)\bigg(\frac{2\sqrt{2}}{3}\bigg)\bigg(  \frac{1}{3}\bigg) = \frac{4\sqrt{2}}{9}
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 3
    Last Post: December 5th 2010, 10:15 PM
  2. Replies: 6
    Last Post: October 15th 2010, 01:18 PM
  3. Replies: 3
    Last Post: January 12th 2010, 05:19 AM
  4. acute angle
    Posted in the Algebra Forum
    Replies: 2
    Last Post: February 27th 2008, 11:48 AM
  5. Acute angle
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: April 2nd 2007, 09:31 AM

Search Tags


/mathhelpforum @mathhelpforum