The circle represents a plane figure whose points are equidistant from its center, and diameter of a circle – the piece passing through this center and connecting two most remote points of a circle. Diameter it becomes frequent that size which allows to solve the majority of problems in geometry of finding of a circle.
Instruction
1. For example, to find circle length, it is enough to determine the known diameter in the form of basic data. Set that diameter of a circle, equal N is known to you, and draw a circle according to these data. As diameter connects two points of a circle and passes at the same time through the center, therefore, circle radius will always be equal to value of half diameter, that is r = to N/2.
2. Use for finding of length or any other size a mathematical constant π. It represents the attitude of value of length of a circle towards value of length of diameter of a circle and in geometrical calculations is accepted equal π ≈ 3.14.
3. To determine circle length, take standard formula L = π*D and substitute value of diameter of D = to N. As a result diameter increased by size of 3.14 will show the approximate length of a circle.
4. In a case when it is required to determine not only length of a circle, but also its area, also use value of a constant π. Only this time use other formula according to which the area of a circle is defined as the radius length built a square, and increased by number π. According to formula looks as follows: S = π * (r^2).
5. As in basic data it is defined that r radius = N/2, therefore, the formula of the area of a circle changes: S = π * (r^2) = π * (N/2) ^2). As a result, if you substitute value of the known diameter in a formula, you receive the required area.
6. Do not forget to check in what units of measure it is necessary to determine length or the area of a circle. If in basic data it is defined that diameter is measured in millimeters, the area of a circle also has to be measured in millimeters. For other units - cm2 or sq.m calculations are made similarly.