How to find the area, knowing the diameter

Objectives to calculate the area of a circle often meet in the school geometry course. To find the area of a circle, you need to know the length of the diameter or radius of a circle in which it is enclosed.

You will need

• - the length of the diameter of the circle.

Instruction

1. A circle is a figure in the plane consisting of a plurality of points disposed in the same distance from another point called the centre. A circle is a flat geometric figure, represents the set of points enclosed in a circle which is the boundary of the circle. Diameter is a segment that connects two points on the circle and passing through its center. The radius is the segment connecting a point on the circle and its center. π — the number "PI", a mathematical constant that is the constant. It shows the ratio of the circumference to the length of its diameter. To compute the exact value of π is impossible. In geometry use the approximate value of this number: π ≈ 3,14
2. The area of a circle equals the product of the square of the radius to the number calculated by the formula: S=NR^2, where S is the area of the circle, R is the length of the radius of the circle.
3. From the definition of the radius, it follows that it is equal to half the diameter. Hence, the formula becomes: S=π(D/2)^2, where D is the length of the diameter of the circle. Substitute in the formula the value of the diameter, calculate the area of a circle.
4. The area of a circle is measured in square units — mm2, cm2, m2, etc. In what units is expressed you received the area of a circle depends on what units was the diameter of a circle.
5. If you need to calculate the area of a ring use this formula: S=π(R-R)^2, where R, r are radii of the outer and inner circumferences of the ring, respectively.