General equation of circle: x+y+dx+ey+f = 0 (d+e-4f > 0), center: (-D/2, -E/2), radius: root (D+E-4F)/2.
1, several common cases about the intersection of straight lines and circles. If the intersection point is not found, it is directly determined that the straight line intersects the circle, which is usually converted into a comparison of the distance and radius from the circle to the straight line. By finding the intersection of a straight line and a circle, we can solve the equations simultaneously, and then we can find the chord length. Usually Pythagorean theorem mainly uses the equal distance from the original center to two intersection points to find the original center. Firstly, the equations are solved simultaneously, and then the coordinates of two points are obtained. According to the situation that the center of the circle is on a straight line
2. The diameter of a circle is proportional to a square with the same diameter and side length. The area ratio of this circle and this square is the same, that is, the square area or perimeter ratio of a circular station is 0.7854 or 0.7858, and the area-volume ratio of a cube and a sphere with the same side and diameter is the same. Multiply the area or perimeter of the square by 0.7854 to get the area and perimeter of the circle with the diameter of one side of the square.
3. Pi is one of the important constants in mathematics. It refers to a mathematical constant representing the ratio of the circumference to the diameter of a circle, which is expressed by the Greek letter π. π is also equal to the ratio of the square of the area and radius of a circle, and the approximate value is about 3. 14 159265359, which is the key value for calculating the geometric shapes such as the circumference of a circle, the area of a circle and the volume of a sphere. It is the first special constant recognized by human beings.