Results 1 to 2 of 2

Thread: trouble reading sin graph, not accurate anymore?

  1. #1
    Newbie
    Joined
    Apr 2010
    Posts
    1

    trouble reading sin graph, not accurate anymore?

    my problem is that though I am aware i can use Rsin(x-a) to express this equation i never get the same answers as the book which uses Rcos(x+a). The book chose to express the equation as Rcos(x+a), however i want to express it as Rsin(x-a) because i am unable to read off the sin graph, it does not work anymore the reading are inaccurate. Can someone represent the equation as Rsin(x-a) and tell me how they got there?

    the books R(cos.. working
    the equation$\displaystyle 7cos(x)-24sin(x)=Rcos(x+a)$

    $\displaystyle R=sqrt(7^2+24^2)=25$

    $\displaystyle cos a=(7/25)or sin a=(24/25)$ this results in a=73.74

    $\displaystyle 7cos(x)-24sin(x)=10$

    $\displaystyle 25cos(x+73.74)=10$

    $\displaystyle cos(x+73.74)=0.4$

    $\displaystyle x+73.74=66.42, 360+/-66.42$

    $\displaystyle x=219.84, 352.68$
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    Joined
    Jun 2009
    Posts
    806
    Thanks
    4
    If you use Rsin(x-a) = R(sina*cosx - cosa*sinx)
    then tan(a) = sin(a)/cos(a)
    Find the value of a.
    Substitute in the equation and find the value of x.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 8
    Last Post: Sep 20th 2011, 12:42 PM
  2. having trouble imaganing this graph
    Posted in the Calculus Forum
    Replies: 3
    Last Post: Jun 18th 2011, 05:46 PM
  3. Having trouble with graph of trig. function
    Posted in the Calculus Forum
    Replies: 3
    Last Post: Nov 1st 2009, 11:06 PM
  4. linear appx/graph reading
    Posted in the Calculus Forum
    Replies: 3
    Last Post: Apr 29th 2008, 01:07 PM
  5. simplify anymore?
    Posted in the Algebra Forum
    Replies: 2
    Last Post: Mar 22nd 2008, 04:35 PM

Search Tags


/mathhelpforum @mathhelpforum