Question

Which is the equation of an ellipse centered at the origin with foci on y-axis, major axis of length 20 and minor axis of length 18?

Answer 1

Centered at the origin means (h,k) =(0,0)

Length of major axis, 2a = 20

That gives, a =10

Length of minor axis, 2b =18

That gives, b=9

And since focii is on the y axis, so its a vertical ellipse of the form

$\frac{(x-h)^2}{b^2} + \frac{(y-k)^2}{a^2} =1$

Substituting the values of a and b, we will get

$\frac{x^2}{81}+\frac{y^2}{100}=1$

Answer 2

Answer:

Option C

x^2/81+y^2/100=1