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8.4 ELLIPSES. Definition / featuresStandard form / features graphDeriving formulaFinding equation given featuresRewriting in standard form. Definition of ellipse. An ellipse is the set of points in a plane such that the sum of the distances from two fixed points (called foci) is constantSee
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1. Quiz review Circle equation: (x – h)2 + ( y – k)2 = r2
Recall relevant vocab: diameter, tangent
For parabolas, either: y = a(x – h)2 + k
OR: x = a(y – k)2 + h
For parabolas, a = 1/4p, where p is the distance from the VERTEX to the focus and to the directrix
FOR BOTH TYPES OF CONICS:
- Given equation, find the features
- Given some features, find the equation
- Rewrite an equation in standard form (use completing the square)
ALSO
- know the distance and midpoint formula, review slope formula
- Be able to show that segments are congruent, parallel, or perpendicular, or that one segment bisects another!
2. 8.4 ELLIPSES Definition / features
Standard form / features + graph
Deriving formula
Finding equation given features
Rewriting in standard form
3. Definition of ellipse An ellipse is the set of points in a plane such that the sum of the distances from two fixed points (called foci) is constant
See graph on board
Other features of ellipse:
- center
- major axis + endpoints
- minor axis + endpoints
4. Standard form of ellipse The standard form of an ellipse is:
(x – h)2 + (y – k)2 = 1
a2 b2
Where (h,k) are the coords of the center
a is ˝ the length of the major axis
b is ˝ the length of the minor axis
NOTE that a and b can switch places depending on the orientation of the ellipse!
That is, if the ellipse is horizontally oriented (see board) then “a2” will be underneath the x-term… if the ellipse is vertically oriented, a2 will be underneath the y-term
5. a, b, c The other feature of the ellipse, the foci, can be found using a and b
We call c the distance from the center to a focus
The relationship between a,b and c is:
c2 = a2 – b2
So if we know a and b we can find the coordinates of the foci
6. Example 4-3a