# Advice 1: How to find the diameter

The diameter is a line that connects two points a curved shape and passes through its center. In many applied problems it is required to find the diameter of a circle or sphere. The diameter of a circle to find its radius, length and area of a circle. The diameter of the ball find the radius, volume and surface area.
Instruction
1
The diameter of a circle or sphere, if their radii can be found, knowing that the diameter is two times the radius. Thus, for finding the diameter and radius, have radius multiplied by two:
D = 2*R, where R is the radius of the shape.
2
The diameter of a circle if you know its length can be found by the formula:
D = L/PI where L is the circumference, PI is a constant approximately equal to 3.14.
3
The diameter of a circle if you know its area, you can find the formula:
D = 2*(S/PI)^1/2, where S is the area of a circle.
4
The diameter of the ball, if known, its volume can be find using the formula:
D = (6V/PI)^1/3, where V is the volume of a sphere.
5
If you know the surface area of a sphere, its diameter can be determined by the formula:
D = (S/PI)^1/2, where S is the surface area of a sphere.
Note
^1/2 is actually the square root;
^1/3 is the cube root extraction.

# Advice 2 : How to find the diameter of a circle

The circle is called a geometric figure in the plane consisting of all points in this plane are equidistant from a given point. Given the point is called the center of the circle, and the distance at which points of a circle are its center, radius of the circle. The region of the plane bounded by a circle called the circle.There are several methods of calculating the diameter of a circle, the choice of the specific depends on the available original data.
Instruction
1
In the simplest case, if you construct a circle of radius R, then its diameter will be equal to
D = 2 * R
If the radius of the circle is not known, but is known for its length, the diameter can be calculated according to the formula of length of circumference
D = L/N where L is the length of the circumference, N is the number of P.
The diameter of the circle can be calculated by knowing the area of a circle it limited
D = 2 * v(S/P), where S is the area of a circle, N is the number of P.
2
In special cases the radius of the circle can be found if it is described or inscribed in a triangle.
If the circle inscribed in a triangle, then its radius is given by
R = S/p where S is the area of a triangle, p = (a + b + c)/2 – properiter triangle.
3
For the circledescribed about a triangle, the formula for the radius has the form
R = (a * b * c)/4 * S, where S is the area of a triangle.

# Advice 3 : How to determine the diameter of the circle

The segment connecting two distinct points lying on the same circle, called the "chord" and the chord passing through the center of the circle, has another name - "diameter". This chord has a maximum for the circle length, which can be calculated in several ways, using basic definitions and correlations.
Instruction
1
The easiest way to determine the diameter (D) circumference can be used in the case when you know the radius (R) of the circle. By definition, the radius is the segment connecting the center of the circle with any point lying on the circle. From this it follows that the diameter be two sections, the length of each of which is equal to the radius: D=2*R.
2
Use to calculate the diameter (D) ratio called PI, if you are aware of the length of the perimeter (L). Perimeter for a circle is called the circumference and the number PI expresses a constant ratio between the diameter and the length of a circle in Euclidean geometry, the division of the perimeter of a circle to its diameter always equals PI. Means for finding the diameter and circumference you need to divide this constant: D=L/π.
3
From the formula of finding the area of a circle (S) it follows that to find the diameter (D) you should find the square root of the result of dividing the area by PI and double the value obtained is: D=2*√(S/π).
4
If the circle described by the rectangle and the length of its side is known, there is nothing to calculate there is no need in such a rectangle can be a square, and the length of its side is equal to the diameter of the circle.
5
In the case of circle inscribed in a rectangle the length of the diameter is the same as the length of its diagonal. To identify it with the known width (H) and height (V) of the rectangle, you can use the Pythagorean theorem since the triangle formed by the diagonal, width and height will be rectangular. From theorem it follows that the length of the diagonal of the rectangle, and hence the diameter of a circle is equal to the square root of the sum of squares of width and height: D= √(H2+V2).

# Advice 4 : How to find the diameter knowing the circumference

The number "PI" is the ratio of the length of a circle to its diameter. It follows that the circumference is equal to "PI d" (C = π*D). Based on this ratio it is easy to deduce the formula for inverse proportion, i.e. D=C/π.
You will need
• calculator.
Instruction
1
To find the diameter of a circle, knowing its length, divide the circumference by the number PI (π) equal to approximately three point fourteen hundredths (3,14). The value of diameter does this result in the same units of measurement as the circumference. This formula can be written in the following form:D=C/π where:circumference,π is the number PI, approximately equal to 3.14.
2
Primeralinea the equator of the Earth is approximately equal to 40,000 km. What is equal to the diameter of the Earth?Solution: 40000/3,14=12739 (km).Answer: the diameter of the earth is approximately 12740 kilometres.
3
For a more accurate calculation of the diameter of a circle, use a more accurate representation of "PI", for example: 3,1415926535897932384626433832795. Of course it is not necessary to use all the signs of the numbers, for most engineering calculations is enough 3,1416.
4
When calculating the diameter of a circle based on its length, please note that many (especially scientific) calculators have a special key for entering the number "PI". This is indicated by a button that says on (over, under) her "π" or something similar. For example, in virtual the calculator in Windows, the appropriate button is designated as pi. The use of a special key allows to significantly speed up the entry of "PI" and to avoid errors when entering. In addition, the PI stored in the memory of the calculator, the provided with the maximum possible for each device accuracy.
5
Sometimes the measurement of the circumference is almost the only acceptable way to know its diameter. This is especially true of tubes and cylindrical structures, "with no beginning and no end."
6
To measure the circumference (cross-section) cylindrical object, draw a string or rope of sufficient length and wrap it around the cylinder (in one turn).
7
If you need a very high accuracy of measurements or the subject has a very small diameter, then wrap the cylinder several times, and then divide the length of the strands (ropes) on the number of revolutions. In proportion to the number of turns will increase the accuracy of the measurement of the circumference, and, respectively, and calculating its diameter.
Search