Calculation of the area of a circle and its parts belongs to tasks in geometry of the 9th class. The ability to solve them to you can be required not only to help your child with geometry, but also for performance of technical tasks at work or with life. Applying a formula of calculation of the area of a circle, it is possible to calculate, for example, consumption of materials according to drawings at construction of the round pool or to calculate the cross-sectional area of an electric cable when performing electric installation work.

## It is required to you

- For finding of the area of a circle:
- - geometrical formula of finding of the area of a circle of S = Pkhr2, where:
- - S - area of a circle;
- - П - number "пи", it is constant and equal to value 3.14;
- - r - circle radius.
- For finding of the area of the sector of a circle:
- - geometrical formula S=P x r2/360 ° x n °, where:
- - S - area of the sector of a circle;
- - П - number "пи", it is constant and equal to value 3.14;
- - r - circle radius;
- - n - value of the central corner of the sector in degrees.

## Instruction

1. Measure circle radius by means of a ruler. Calculate value of the area of a circle on a geometrical formula of finding of the area of a circle (the area of a circle is equal to the work of number "пи" and a circle radius square).

2. Build value of length of radius of a circle a square for finding of the area of a circle, increase the received number by number "пи" (its value is constant and equal to 3.14). So, having used a formula, you will find the area of a circle.

3. Measure a sector corner in degrees by means of a protractor. You already know the area of a circle. Calculate value of the area of the sector of a circle on a geometrical formula (the area of the sector of a circle is equal to the work of the area of a circle with r radius on the relation of a corner of the sector of n ° to a corner of a full circle, i.e. 360 °).

4. Divide value of the area of a circle into 360 and increase by sector corner size in degrees. So you will find the size of the area of the sector of a circle on a-degree measure of its corner.