1, first determine the length and width of the rectangle, mark the midpoint of each side length, and connect the midpoints of each side to form a diamond in the rectangle.

2. Then mark the midpoint of each side length of the diamond, starting from the midpoint in the upper left corner, and mark it with the serial number 1234 in zigzag order.

3. Connect the midpoint directly below the rectangle with point 1 point 2, connect the midpoint directly above the rectangle with point 3 and point 4, and mark the two points with 5 and 6.

4. Draw an arc with point 6 as the center, connection point 2 as the center, point 5 as the center and connection point 1 as the center.

5. Draw an arc with the midpoint directly below the rectangle as the center, the connection point 1 as the center and the connection point 4 as the center.

1, let F 1 and F2 be the two focuses of ellipse C, and P is any point on C. If straight line AB intersects ellipse C at point P and A and B are located on both sides of straight line P, then ∠APF 1=∠BPF2.

2. Let F 1 and F2 be the two focal points of ellipse C, and P be any point on C. If the straight line AB is the normal of C at point P, then AB divides F1PF2 equally.

3. In the plane rectangular coordinate system, high school textbooks describe ellipses with equations. 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.

4. when the focus is on the y axis, the standard equation is: y 2/a 2+x 2/b 2 =1(a > b > 0), where a>0 and b>0. The larger one of A and B is the long semi-axis length of the ellipse, and the shorter one is the short semi-axis length (the ellipse has two symmetrical axes, which are cut by the ellipse and have two line segments.

5. Half of them are called the long and short axis or the half-long and half-short 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. The relationship between focal length and long and short semi-axes: B 2 = A 2-C 2, the directrix equations are X = A 2/C and X =-A 2/C, and c is the half focal length of an ellipse.

6. Unified form of standard equation. The area of an ellipse is πab. An ellipse can be regarded as the stretching of a circle in a certain direction, and its parameter equations are: x=acosθ, y=bsinθ.

7. The tangent of the standard ellipse at (x0, y0) is: xx0/a 2+yy0/b 2 = 1. The slope of the ellipse tangent is -b 2x0/a 2y0, which can be obtained by very complicated algebraic calculation.