View Full Version : Find standard form of ellipse given center and foci
jordo6889
Oct 26, 2009, 01:55 PM
Find the equation in standard form of an ellipse with center at (0,0) minor axis of length 12, and foci at (0,-8) and (0,8).
Nhatkiem
Oct 26, 2009, 07:25 PM
Find the equation in standard form of an ellipse with center at (0,0) minor axis of length 12, and foci at (0,-8) and (0,8).
the general standard form of an ellipse is
(\frac{x}{a})^2+(\frac{y}{b})^2=1
where a and b are the radii of your major and minor axis.:)
ebaines
Oct 27, 2009, 07:20 AM
Nhatkiem's suggestion will let you determine the value of b, but to find a you need to use the fact that :
a^2 - b^c = F^2
where F is the distance from the center of the ellipse to the focal point(s).
Also, don't forget that a and b are the lengths of the semi-major and semi-minor axes, respectively.
Nhatkiem
Oct 27, 2009, 09:13 AM
Nhatkiem's suggestion will let you determine the value of b, but to find a you need to use the fact that :
a^2 - b^c = F^2
where F is the distance from the center of the ellipse to the focal point(s).
Also, don't forget that a and b are the lengths of the semi-major and semi-minor axes, respectively.
hmm I always thought the definition for minor/major axis were dependent one which ones were longer, meaning the definition of a and b were interchangeable depending on lengths:confused: Been a while since I've done this ellipse.. boo.
ebaines
Oct 27, 2009, 09:25 AM
hmm I always thought the definition for minor/major axis were dependent one which ones were longer, meaning the definition of a and b were interchangeable depending on lengths:confused: Been a while since ive done this ellipse .. boo.
Yes - you are right - the a dimension is along the x axis, and the b along the y axis. If a > b then a is the semi-major axis length and b is the semi-minor length. I jumped ahead a bit and said that a is the semi-major and b the semi-minor, essentially giving away that the ellipse is stretched horizontaly (not vertically). The point I was trying to make was to distinguish between the minor axis length and the semi-minor laxis ength.