1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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: When we use standerd Equation of an ellipse

  1. Apr 21, 2010 #1
    Hi

    when we use standerd Equation of an ellipse

    here 2 formula 1 and 2 when we use 1 and when we use 2

    hlep me
     

    Attached Files:

  2. jcsd
  3. Apr 21, 2010 #2

    CompuChip

    User Avatar
    Science Advisor
    Homework Helper

    Errr... what's the difference, except that a is called b and b is called a in (2)?
     
  4. Apr 21, 2010 #3
    when we say a is called b and b is called a in the queation

    i mean in queation how we nowthe solve will be by formula 1 or 2

    help me >>
     
  5. Apr 21, 2010 #4

    Mark44

    Staff: Mentor

    The two formulas shown in the page you scanned are needlessly complicated. Only one equation is needed for an ellipse.
    [tex]\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1[/tex]

    If a > b, the major axis is along the x axis.
    If a < b, the major axis is along the y axis.

    Ex. 1
    [tex]\frac{x^2}{25} + \frac{y^2}{16} = 1[/tex]
    x-intercepts (vertices) at (5, 0) and (-5, 0).
    y-intercepts at (0, 4), and (0, -4).
    Foci at (3, 0) and (-3, 0).

    Ex. 2
    [tex]\frac{x^2}{16} + \frac{y^2}{25} = 1[/tex]
    x-intercepts at (4, 0) and (-4, 0).
    y-intercepts (vertices) at (0, 5), and (0, -5).
    Foci at (0, 3) and (0, -3).
     
  6. Apr 21, 2010 #5
    The b2 and a2 (depending on position) tell you the major and minor axis and which way to ellipse will be (like vertical or horizontal)

    keep in mind: a cannot equal b because then it will be a circle not an ellipse.
     
    Last edited: Apr 21, 2010
  7. Apr 21, 2010 #6

    Mark44

    Staff: Mentor

    A circle can be thought of as a special case of the ellipse, where the major and minor axes are equal.
     
  8. Apr 21, 2010 #7
    Well yes, but it's generally not.
     
  9. Apr 22, 2010 #8

    CompuChip

    User Avatar
    Science Advisor
    Homework Helper

    Ellipses are generally not circles, indeed.
    But all circles are ellipses.

    Just like not all rectangles are squares, but all squares are rectangles.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook