Question

Why is this equation:
`((x-2)^(2))/(24) + ((y+5)^(2))/(29)=1` an ellipse and not a circle?

Usually, you can tell if it's an ellipse because the coefficients of x and y are different. Here, though, they're the same, yet every website is telling me it's an ellipse and not a circle. Why is that?


THANKS!

Answer 1

well, your observation is correct, for the form

Ax² + Bx + Cy² + Dy + E = 0

if the coefficients are the of x² and y² are different and the same sign then we have an ellipse, hmmm I usually see a circle as an ellipse with equal major and minor axes, because is basically just that.

However, the rational form you have is that of an ellipse indeed, we can change it about to the form above and you'll see it so.

Just bear in mind that for the rational form for conics

if both fractions are positive and their denominator different, is an ellipse

if both fractions are positive and their denominator equal, is a circle

if one of the fractions is negative, then we have a hyperbola, and on a hyperbola the traverse axis is always the denominator with the positive fraction, so if the denominator is under the "x" fraction, then the traverse axis is horizontal, if under the "y" fraction, then vertical.

based on that fraction, is an ellipse with a center at (2 , -5).

now, the larger denominator is 29 and it's under the "y" variable, that means the major axis is in the direction of the y-axis, so is a vertical ellipse if you wish. Check the picture below.