Instruction

1

Let there be a circle. If the radius of this

- to know the radius of a simple measurement of the radius of its circumference,

- if you know the circumference of this

- can you describe a square about a circle, then its radius is equal to half the side of the square.

**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.

2

From the school course of geometry known theorem - area

S = P*R*R

**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.

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.