Extended data:
The product of normal slope and tangential slope is-1, that is, the normal slope and tangential slope are expressed by α and β respectively, so there must be α*β=- 1. The normal can be expressed by a linear equation, that is, the normal equation. There is a direct conversion relationship with the derivative.
Normal equation of curve at point (x0, y0)? ,? ; The locus of the moving point P whose sum of the distances between two points on a plane is equal to a constant () is called an ellipse.
Namely:? These two fixed points are called the focal points of the ellipse, and the distance between the two focal points is called the focal length of the ellipse.
Is the moving point of an ellipse. The chord obtained by cutting the ellipse into a line coincident with the line connecting the two focal points is the long axis and the length is. The ellipse cuts a straight line, which bisects the straight line connecting the two focal points vertically. The chord is the short axis and the length is. ? Can be.
In the plane rectangular coordinate system, the ellipse is described by an equation, and the "standard" in the elliptic standard equation means that the center of the circle is at the origin and the axis of symmetry is the coordinate axis.
According to the coordinate axis where the focus is located, the ellipse has two standard equations:
The sum of the distances from any point on the ellipse to F 1 and F2 is 2a, and the distance from F 1 to F2 is 2c. What about b in the formula? =a？ -c？ . B is a parameter set for writing convenience.
Also: if the center of the circle is at the origin, but the position of the focus is not clear on the X axis or Y axis, the equation can be set to mx? +ny？ = 1。 0, n>0, m≠n). Unified form of standard equation.
References:
Baidu encyclopedia-ellipse