Typically, the geometry of the tasks as well asin practical matters, given the diameter of the circle, and you want to find the length. But there are situations when you need to reverse - known length of the circle, and it is necessary to calculate the rest of its parameters.

In math class, or drawing may be necessary to know the radius of the circle before it to plot. In practical life, too, there are situations.

For example, do you know the size of a hat, and want to build it a pattern.

You will need

- Compass
- The concept of the radius, diameter and circumference
- Formula circumference

instructions

1

Remember that such a circumference, and how it is measured. In practical life this usually apply flexible measuring devices, such as tape measures, or roulette. If you need to know **diameter** the cylinder base, you can first make it scan, circling the base and constructing a lateral surface. The circumference of the base in this case will be equal to the length of the base.

2

Recall, according to what formula is calculated the circumference. Mark the length of the circumference as C, its radius - like the R, **diameter** - D. a circumference of radius equal to twice the product of the number of C = 2 R??. Remember what **diameter** circumference. This is twice the radius.

3

Find twice the radius of the circle. 2R = C / ?. Thus, D = C / ?. Remember, what is equal to the number?. It is 3, 14. Divide the circumference by that number. To determine the radius of the need to obtain private divide by 2. Draw the circle on the resulting radius.

4

Hearing radius length, and can define an areacircle. This must be done, if by doing a pattern a round hat, you want to calculate. How much material will need. Mark the area of a circle as S. It will be equal to the number? Multiplied by the square of the radius.