Question

Points A and B are the foci of a conic section. Two points on the conic section, C and D, have distances to the foci A and B as shown.
CA=5
CB=10
DA=8
In order for the points C and D to be on the same ellipse, the distance would have to equal ?

Answer 1

Ellipse - Sum of the two distances from the foci is constant.

d(CA) + d(CB) = 5 + 10 = 15

d(DA) + d(DB) = 8 + ?? = 15

Answer 2

Thank you!