When the focus is on the X axis, the standard equation of the ellipse is: X 2/A 2+Y 2/B 2 =1,(a>b>0);

When the focus is on the Y axis, the standard equation of the ellipse is: Y 2/A 2+X 2/B 2 =1,(a>b>0);

In which a>0 and b>0. The larger one of A and B is the long semi-axis of an ellipse, and the shorter one is the short semi-axis (the ellipse has two symmetry axes and is cut into two line segments by the ellipse, and half of them are called the long semi-axis and short semi-axis or semi-long semi-axis and semi-short semi-axis of the ellipse respectively) when A >; B, the focus is on the X axis, and the focal length is 2 * (A 2-B 2) 0.5. Relationship between focal length and long and short semi-axes: B 2 = A 2-C 2.

The alignment equations are x = a 2/c and x =-a 2/c.