By EasyHow

How to calculate the area of a circle

To solve this problem, you must first introduce the concept of the number P (PI). The number P is a mathematical constant that expresses the ratio of the circumference to the diameter of this circle. P is an infinite non-periodic decimal fraction, its value is constant for all circles and is approximately 3,14159265358979... To solve practical problems is usually enough values of 3.14Area of the circle is one of the geometrical quantities determining its size. For finding this value is sufficient to know the radius of the circle and the number P (PI).

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Instruction

Let there be a circle. If the radius of this circle we do not know, you can find it in several ways:
- to know the radius of a simple measurement of the radius of its circumference,
- if you know the circumference of this circle, its radius can be calculated according to the formula R = L/2P, where L is the length of the circumference,
- can you describe a square about a circle, then its radius is equal to half the side of the square.

From the school course of geometry known theorem - area of a circle is equal to half of the length of work limiting its circumference to the radius.
S = P*R*R

Note

There are several alternative formulas to calculate the area of a circle, all of them by way of transformation are reduced to a common formula, but may be useful in specific situations.

The area of a circle inscribed in a triangle.
S = P*((p-a)*tg(A/2))2, where p is pauperised, a, and A - side and the opposite angle of the triangle, respectively, (p-a)*tg(A/2) - radius of inscribed circle

The area of a circle described about the triangle.
S = P * (a/(2*sin(A)))2, where a and A - side and the opposite angle of the triangle respectively, a/(2*sin(A)) is the radius of the circumscribed circle.