Question

find the coordinates for the foci.

x*2/16 + y*2/81 = 1

Answer 1

Formula for the focal distance of an ellipse
a^2 = b^2 + c^2
81 = 16 + c^2
c^2 = 65
c = √65
Since this is a vertical oriented ellipse, have the focii on the major axis.
(0, √65), (0, -√65)