2. Pi represents the multiple relationship between (perimeter) and (diameter) in the same circle, which is represented by the letter (π) and the approximate value is (3. 14), with two decimal places reserved.

3. You can draw (countless) diameters in the same circle; If a circle with a diameter of 10 cm is drawn with a compass, the distance between two feet of the compass should be (5) cm.

Draw the largest circle in a rectangle with a length of 6 cm and a width of 4 cm. The circumference of this circle is (12.56 cm) and the area is (12.56cm).

5, a circle, the diameter of the outer circle.

The pi of the extended data is also equal to the ratio of the area of the circle to the square of the radius. Accurate calculation of geometric shapes such as circle perimeter, circle area and sphere volume is the key value. In the analysis, π can be strictly defined as the smallest positive real number x satisfying sin x = 0.

When Liu Hui, a mathematician in China, annotated Nine Chapters Arithmetic (263), he got the approximate value of π only by inscribing a regular polygon into a circle, and also got the value of π accurate to two decimal places. His method is called the secant circle method by later generations. He used the method of secant circle until the circle inscribed the regular polygon of 192, and got the π ≈ radical sign of 10 (about 3. 14).