an ellipse has foci f1(9, 0) and f2(11, 6), and the point (1, 6) is on the ellipse. identify the constant sum for the ellipse.
a 20
b 10
c 0
d 100

The first step is to find the distance from the given point to each of the two foci as follows:
Distance D1:
(D1)^2 = (9-1)^2 + (0-6)^2 = 100
D1 = 10
Distance D2:
(D2)^2 = (11-1)^2 + (6-6)^2 = 100
D2 = 10

The constant sum is the summation of the two distances as follows:
constant sum = D1 + D2 = 10 + 10 = 20

The correct choice is:
a) 20