Results 1 to 3 of 3

Math Help - Dont understand how this works

  1. #1
    Newbie
    Joined
    Feb 2010
    Posts
    10

    Dont understand how this works

    Suppose y varies directly as the square of x and inversly as the cube of w. We know that y=9 when x=2 and w=1. Find y when x=4 and w=2.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member pflo's Avatar
    Joined
    Apr 2009
    From
    Albuquerque, NM
    Posts
    155
    Thanks
    7
    Quote Originally Posted by brianfisher1208 View Post
    Suppose y varies directly as the square of x and inversly as the cube of w. We know that y=9 when x=2 and w=1. Find y when x=4 and w=2.
    The first sentence is telling you the following formula is correct (where k is the 'constant of variation'): y=k\frac{x^2}{w^3}

    Use the information in the second sentence to solve for k. Once you know that, you can use the equation to get the answer to the third sentence.
    Last edited by pflo; February 26th 2010 at 10:29 PM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,553
    Thanks
    1424
    Quote Originally Posted by brianfisher1208 View Post
    Suppose y varies directly as the square of x and inversly as the cube of w. We know that y=9 when x=2 and w=1. Find y when x=4 and w=2.
    y \propto x^2, so y = k_1x^2.

    Substitute x and y to find k_1.


    y \propto \frac{1}{w^3}, so y = \frac{k_2}{w^3}.

    Substitute w and y to find k_2.



    Then you should be able to finish the question.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. please help i dont really understand this!
    Posted in the Business Math Forum
    Replies: 1
    Last Post: September 7th 2010, 05:24 PM
  2. Replies: 2
    Last Post: July 14th 2010, 10:26 PM
  3. I don't understand how this works..
    Posted in the Math Topics Forum
    Replies: 1
    Last Post: November 3rd 2009, 06:05 AM
  4. What I dont understand is
    Posted in the Calculus Forum
    Replies: 2
    Last Post: March 31st 2008, 06:57 PM
  5. I dont understand this..
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: August 18th 2007, 04:48 PM

Search Tags


/mathhelpforum @mathhelpforum