Focus (geometry)

With the help of focal points - usually two - can be constructed of various geometric curves, especially conic sections.

So an ellipse is the set of points which, for the most part referred to as having the two focal points of a certain distance sum. The distance of the two focal points to the center of the ellipse, usually denoted by e, is called linear eccentricity. If we subtract a point on the ellipse, the straight line connecting the two foci, so the two lines are mirror image of the tangent at the point ( reflectivity ).

Also, a hyperbola has two foci; in this case, is constant for each point of the hyperbola, the difference in distance from these points.

A parabola has only one focus, because it arises as a limiting case of an ellipse, if you can move to infinity the second focal point. The focal point of a parabolic equation ( vertex at the origin ) is given by. The reflection property is the basis of the parabolic mirror.

The circle can be considered as a further limiting case of an ellipse, in which its two foci coincide ( in the center of the circle ).

• Plane Geometry