How to calculate the diameter of a circle?

To begin with, let's understand what a circle is and what is its difference from a circle. Take a pen or pencil of red color and draw a regular circle on a piece of paper. Paint the entire middle of the figure with a blue pencil. A red outline indicating the boundaries of a figure is a circle. But the blue content inside it is a circle.

The dimensions of the circle and circle are determined by the diameter. On the red line denoting the circle, mark the two points so that they are a mirror image of each other. Connect them with a line. The segment must pass through a point in the center of the circle. This segment, which connects the opposite parts of the circle, is called in geometry by diameter.

A segment that extends not through the center of a circle, but closes with its opposite ends, is called a chord. Consequently, the chord that passes through the point of the center of the circle is its diameter.

The diameter is denoted by the Latin letter D. The diameter of the circle can be found from such values as the area, length and radius of the circle.

The distance from the central point to the point deposited on the circle is called the radius and is denoted by the letter R. Knowing the radius value helps to calculate the diameter of the circle by one simple action:

D = 2 * R

For example, the radius is 7 cm. Multiply 7 cm by 2 and get a value of 14 cm. Answer: D of the given figure is 14 cm.

Sometimes it is necessary to determine the diameter of a circle only along its length. Here it is necessary to apply a special formula that helps determine the circumference of a circle. The formula L = 2 Pi * R, where 2 is a constant value (constant), and Pi = 3.14. And since it is known that R = D * 2, the formula can also be represented in another way

L = Pi * D

D = L / Pi

This expression is also applicable as a formula for the diameter of a circle. Substituting the quantities known in the problem, we solve the equation with one unknown. Let's say the length is 7 m. Hence:

D = 7/3, 14

D = 21, 98

Answer: the diameter is 21.98 meters.

If you know the value of the area, you can also determine the diameter of the circle. The formula used in this case looks like this:

D = 2 * (S / Pi) * (1/2)

S - in this case the area of the figure. Suppose, in the problem, it is equal to 30 square meters. M. We get:

D = 2 * (30/3, 14) * (1/2) D = 9, 55414

When the value indicated in the problem is equal to the volume (V) of the ball, the following formula for finding the diameter is used: D = (6 V / Pi) * 1/3.

Sometimes it is necessary to find the diameter of a circle inscribed in a triangle. For this, from the formula, we find the radius of the circumscribed circle:

R = S / p (S is the area of the given triangle, and p is the perimeter divided by 2).

The result is doubled, taking into account that D = 2 * R.

Often find the diameter of the circle is also in everyday life. For example, when determining the size of a ring, which is equivalent to its diameter. To do this, you need to wrap the finger of the potential ring owner with a thread. Mark the points of contact of the two ends. Measure the length from point to point with a ruler. The resulting value is multiplied by 3.14, following the formula for determining the diameter for a known length. So, the statement that knowledge in geometry and algebra in life is not useful, does not always correspond to reality. And this is a serious reason to take a more responsible attitude to school subjects.