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

Option C

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

Answer 2

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

`image`

Substituting the values of a and b, we will get

`(x^2)/(81)+(y^2)/(100)=1`