Eccentricity of an ellipse

Question

Find the eccentricity of an ellipse with foci (+-9,0) and vertices (+-10,0).

Answer 1

Distance between foci is 2C.

2C =√((9+9)²+(0-0)²)

   = 9

C =9/2

 

Distance between vertices is 2a.

2a =√((10+10)²+(0-0)²)

   = 10

a=5

Eccentricity of an ellipse is e = c/a

e = (9/2)/5

   = 9/10

    = 0.9