Instruction
1
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.
- 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 of a circle is equal to half of the length of work limiting its circumference to the radius.
S = P*R*R
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.
