Tasks on calculation of the area of a circle often meet in a school course of geometry. To find the area of a circle, it is necessary to know length of diameter or radius of a circle into which it is put.
It is required to you
- - length of diameter of a circle.
Instruction
1. A circle — the figure on the plane consisting of a set of the points removed on identical distance from other point called by the center. A circle — the flat geometrical figure, represents a set of the points concluded in a circle which is circle border. Diameter is the piece which is connecting two points on a circle and passing through its center. Radius is the piece connecting a point on a circle and to its center. π — number "пи", a mathematical constant, a constant. It shows the circle length attitude to length of its diameter. It is impossible to calculate exact value of number π. In geometry use approximate value of this number: π ≈ 3.14
2. The area of a circle is equal to the work of a square of radius on number and is calculated on a formula: S=πR^2 where S is the area of a circle, R is circle radius length.
3. Follows from determination of radius that it is equal to a half of diameter. Therefore, the formula takes a form: S=π (D/2) ^2, where D — length of diameter of a circle. Substitute value of diameter in a formula, calculate the area of a circle.
4. The area of a circle is measured in units of area — mm2, cm2, sq.m , etc. In what units the area of a circle received by you is expressed, depends on in what units diameter of a circle was given.
5. If you need to calculate the area of a ring, use a formula: S=π(R-r) ^2 where R, r are radiuses of external and internal circles of a ring respectively.