http://www.youtube.com/watch?v=7UD8hOsvaI
The foci of an ellipse are always on the major axis:
major axis = 2a
in this case!
Foci are ALWAYS on the major axis
Sum of the focal radii
length of major axis
In general, the equation ofany ellipse with centreat the origin:
a = centre to leftOr right side
b = centre to top or bottom
c = centre to focus
Example
x2 + y2 49 16 = 1
Remember: The sum of the focal radii is constant
Example
x2 + y2 4 20 = 1
This is a special kind of ellipse:
x2 + y2 = 116 16
Sometimes we must first convert to standard form
x2 + 4y2 = 64
Bring in inequalitiesx2 + y2a2 b2 ≤1
<1x2 + y2a2 b2
≥1
>1
x2 + y2a2 b2
x2 + y2a2 b2
page 333 335: 5, 6, 7, 9, 12, 13, 17
page 323 327: 1, 2, 3, 6, 7, 11, 15
page 329: 18, 19, 20