Results 1 to 2 of 2

Math Help - How do you find areas?

  1. #1
    Newbie
    Joined
    Jan 2007
    Posts
    19

    How do you find areas?

    Find the area of the region enclosed by the curves y=x+9, y=22-x^2, x=-1, and x=2, accurate to two decimal places.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by asnxbbyx113 View Post
    Find the area of the region enclosed by the curves y=x+9, y=22-x^2, x=-1, and x=2, accurate to two decimal places.

    First thing's first: draw the graphs. This will let you know which graph is above which. The area of the region enclosed will be the area under the higher graph minus the area under the lower graph. We take the integral between the limits given, that is x=-1 to x=2.

    Plotting the graphs, you will realize that the 22 - x^2 graph is the higher one. So the area between the enclosed region will be:

    int{22 - x^2 - (x + 9)}dx evaluated between x=-1 and x=2
    = int{-x^2 - x + 13}dx
    = -(x^3)/3 - (x^2)/2 + 13x + C

    so the area is:
    A = [-(2^3)/3 - (2^2)/2 + 13(2)] - [-(-1^3)/3 - (-1^2)/2 + 13(-1)] ...Note, we dont have to write the C's in here because they'll cancel anyway.

    => A = -8/3 - 4/2 + 26 - (1/3 - 1/2 - 13)
    = -8/3 - 2 + 26 - 1/3 - 1/2 - 13
    = 15/2 = 7.50 squared units

    The method is right, but double check my computation, 'cause i'm half asleep right now
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Help, integration, find areas
    Posted in the Calculus Forum
    Replies: 3
    Last Post: June 10th 2010, 07:09 AM
  2. find ratio of areas
    Posted in the Geometry Forum
    Replies: 1
    Last Post: April 14th 2010, 09:43 PM
  3. Formula to find segment areas
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: January 14th 2010, 07:29 AM
  4. Find the perimeters and areas of the figure.
    Posted in the Geometry Forum
    Replies: 3
    Last Post: October 21st 2009, 07:52 PM
  5. By comparing areas find the value of a log
    Posted in the Calculus Forum
    Replies: 1
    Last Post: June 15th 2009, 05:01 AM

Search Tags


/mathhelpforum @mathhelpforum