Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Help with Functions

  1. Jan 24, 2005 #1
    Help with Functions!!

    Hi everone this is my first thread and I am looking forward to particitate in PF. Anyways I need help with a question...although I found a solution but I am not sure if it is right..any help would be greatly appreaciated.
    Question - A Norman window has the shape of a rectangle surmounted by a semicircle. If the perimeter of the window is 30ft, express the area A of the window as a function of the width x of the window.
    Solution - 2x+2y=30, solvin for y; y=15/2-x
    A=Rectangle + semicircle
    A=xy + "pi"(x/2)^2
    A=x(15/2-x)+"pi"x^2/4
    A=15x/2-x^2+"pi"x^2/4
    Well....it looks pretty simple but last assignment I did, I got a low mark and I screwed up in many places....so I just want to make sure it doesnt happen again...thanks in advance.
     
  2. jcsd
  3. Jan 24, 2005 #2

    quasar987

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Hi the game, warm welcome to PF ! You have found homework help paradise. :biggrin:

    I'm afraid I disagree with your first equation :eek:.

    You give 2x+2y=30 as the equation of the perimeter. But this looks to me like the equation for the perimeter of a rectangular window! Try working out a new perimeter equation considering the circular higher part of the window.

    And keep in mind when you use the equation of perimeter and area of a circle that you are dealing with a semicircle. Hence you must divide these expressions by half! Ex: the equation of the area and perimeter of the semi-circle are respectively

    [tex]A = \frac{1}{2}\pi r^2[/tex]

    [tex]P = \pi r[/tex]
     
  4. Jan 26, 2005 #3
    Thanks quasar987....I really appreaciate your help....I love PF homework help :)
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook