Graphing Ellipses

Key Questions

  • The standard form of the ellipse is x^2/a^2+y^2/b^2=1x2a2+y2b2=1.

    The easiest way to graph it, is to make a rectangle, centered in the origin, having the horizontal sides with the lenght of 2a2a and the vertical sides with the lenght 2b2b.

    The points (a,0),(0,b),(-a,0),(0,-b)(a,0),(0,b),(a,0),(0,b) are the four vertices of the ellipse.

    It is sufficient now to join the four vertices.

  • It is a rather onerous process to do that. First, you'd need to convert the equation to y=y= form, which means you'd get an ugly looking plus or minus square root function. Also, the processes involved in getting it to this form are very mistake-prone areas.

    However, there is an app in the TI-84 called "Conics" (number 4 under apps) which does let you graph it very easily. Regrettably, this app doesn't have the graph features that the TI-84 has (i.e. Table, Calc Zeroes, etc), and hence is pretty useless unless you want a general picture to see what it looks like. However, I found that this app can be very useful if you forget the formulae for any of your conics. Use it wisely ;-)

Questions