# Search Results for “focus”

##### Focus Directrix Parabola
Try to set the focus and directrix of a parabola so it matches one with a given equation

Tags: parabola, focus, directrix

##### Parabola Directrix
Explore the focus and directrix of a parabola

Tags: parabola, focus, directrix

By Duncan
##### Rolling Parabola
If you roll a parabola along the ground, what curve does its focus trace out? It might look like a parabola, but is it?

Tags: parabola, catenary, focus

##### Parabola Tangent Circumcircle
3 tangents of a parabola form a triangle.  Its circumcircle passes through the parabola's focus.

Tags: parabola, focus, circumcircle

##### Ellipse as locus of circle center
Take two overlapping circles.  Examine the locus of the center of the circles tangential to both. It seems to be an ellipse with foci at the centers of the two circles. Prove it.

Tags: ellipse, conic, focus

##### Parabola Subnormal
The subnormal for a given parabola is constant, and closely related to the focal length.

Tags: parabola, focus, conic

##### proof without words
A proof that the locus of the center of a circle tangential to two nested circles is an ellipse.

Tags: ellipse, focus

By Duncan
##### Focal Triangle
Create a triangle which has 3 points on the circumference of an ellipse, and two sides passing through the foci.  Look at 2 curves formed by the third side: the locus of its center and its envelope.  One is an ellipse, the other is not.

Tags: ellipse, focus

##### Parabola Property
The triangle containing the normal and tangent at a point on a parabola sits inside a semicircle centered at the parabola's focus.

Tags: