The understanding of mathematical circle in the first volume of the sixth grade: the circumference of circle as an example

The quotient of (perimeter) divided by (diameter) of 1. circle is a fixed number, usually called (π/pi), which is approximately equal to (3. 14).

2. If you want to find the circumference of a circle, you must know (c).

A. Diameter and radius

3.π is a decimal (c)

A. finite B. infinite cycle C. infinite acyclic

There is a round flower bed on campus, and its diameter is 4.5 meters. What is the circumference of this flower bed?

Circumference c=πd=3. 14 times 4.5m = 14. 13m.

The perimeter of this garden is 14.438+03 meters.

5. Xiao Qiang runs 15 times around the flower bed with a diameter of 20m every day. How many meters does Xiao Qiang run every day?

The perimeter of the flower bed c=πd=3. 14 times 20m=62.8m 62.8m times 15=942m.

A: Xiao Qiang runs 942 meters every day.

6. The radius of bicycle wheel is15cm. What is the circumference of this bicycle wheel?

Find the diameter: 15*2=30 (cm)

Find the circumference: 30*3. 14=94.2 (cm)

The circumference of this bicycle wheel is 94.2 cm.

I hope this helps.