Um, actually there's one little error;
It's
not
because it's an ellipse streched along the y-axis. Look at page 420, they show two guidelines (in grey); the one on the left shows the guideline for an ellipse having center (0, 0),
foci (0, -c) and (0, c). You followed the guideline for an ellipse having center (0, 0),
foci (c, 0) and (c, 0).
I'll show ya;
"The ellipse having center (0, 0), foci (0, -c) and (0, c), and sum of focal radii 2a has the equation; .............. where "
So, to go back to the orginal question;
What is the equation of the ellipse with foci at (0,-4) and (0,4) ant the sum of its focal radii being 10?
So 10 = 2a, so a = 5 and c = 4. Now plug those values in
;
so b = 3
Since the foci are on the y-axis, the major axis is vertical, so use the appropriate formula;
plug in the values;
Sorry if this is a little lengthy, I just wanted to make sure for the both of us. I actually erased my answers and wrote yours when I saw that ours were different
but then I double checked
Hoorah~