In fact, some people have studied the relationship between perimeter and diameter for a long time and found that the ratio of perimeter to diameter of any circle is a fixed number. We call it pi, which is represented by the letter π(pài). It is an infinite cyclic decimal.

π=3. 14 15926535 ... but in practical application, we usually only take its approximate value, that is, π≈3.

π(pài)=3. 14

1π=3. 14 2π=6.28 3π=9.42 4π= 12.56 5π= 15.7 6π= 18.84 7π=2 1.98

8π=25. 12 9π=28.26 10π=3 1.4