Instruction

1

Let L be the length of the

R = L/2π

Example: length

**circumference**, π a constant, the value of which is constant (π=3.14). Then, to determine the radius given**the circumference**, you need to use the formula:R = L/2π

Example: length

**of a circle**is 20 cm. Then the radius of this**circle**R = 20/2*3.14 = 3.18 cm2

Let the famous S - area

R = √(S/π)

Example: area

**of a circle**. Then, knowing the formula for finding the area**of a circle**(S = πR2), it's easy to withdraw and another to determine the radius**of a circle**:R = √(S/π)

Example: area

**of a circle**is 100 cm2, then its radius is R = √(100/3.14) = 5.64 cm3

If

**the circumference**length of the diameter (a line segment which connects two opposite points**of the circle**, passing through its center), the task of finding the radius is to divide the length of the diameter**of the circle**by 2.Note

Besides the fact that the circle has radius and diameter, it can be constructed chord, Central angle, and inscribed angle. A chord is a segment connecting the 2 points of the circle not passing through its center.

The Central angle is a angle whose apex coincides with the center of the circle. The same inscribed angle is an angle whose vertex lies on any point of the circle.

A circle can also be described around some geometric shapes, or inscribed in it. A circle can be described around an equilateral triangle, square or any other regular polygon. To inscribe a circle in any of these figures.

The Central angle is a angle whose apex coincides with the center of the circle. The same inscribed angle is an angle whose vertex lies on any point of the circle.

A circle can also be described around some geometric shapes, or inscribed in it. A circle can be described around an equilateral triangle, square or any other regular polygon. To inscribe a circle in any of these figures.

Useful advice

If circle is inscribed in an equilateral triangle, a square or another polygon, the radius of this circle equals the square of the polygon is half its perimeter:

R = S/p.

If a circle circumscribed around a triangle, then its radius is set according to the formulas:

R=(a*b*c)/(4*S), where a, b, c be the sidelengths of a triangle, S is the area of the triangle;

R = a/2*sinα, where α is the angle opposite side a.

R = S/p.

If a circle circumscribed around a triangle, then its radius is set according to the formulas:

R=(a*b*c)/(4*S), where a, b, c be the sidelengths of a triangle, S is the area of the triangle;

R = a/2*sinα, where α is the angle opposite side a.