Formula for calculating the circumference of a circle

What is a circle?

A circle is the set of all points lying on a plane and equidistant from a given point (called the center) at a constant distance (called the radius - r). The center of the circle is a fixed point in the middle. Diameter (d): a line segment passing through the center and connecting two points on the circle, equal to d=2r.

Formula for calculating the circumference of a circle when knowing the radius

According to the textbook Connecting knowledge with life, Math 5, Volume 1, Lesson 27, to calculate the circumference of a circle, we take the number 3.14 multiplied by 2 then multiplied by the radius.

C = π x 2 xr

In there:

C is the circumference of the circle

d is the diameter of the circle

r is the radius of the circle

π is a constant (equivalent to 3.14)

Example: Calculate the circumference of a circle with radius 5cm.

Answer: Circumference of circle C = 3.14 x 2 xr = 3.14 x 2 x 5 = 31.4 (cm)

Formula for calculating the circumference of a circle when knowing the diameter

Because the diameter is twice the radius, to calculate the circumference of a circle when knowing the diameter, we take 3.14 multiplied by 2 and then multiplied by the radius.

C = π xd

Example: Calculate the circumference of a circle with diameter 6dm.

Answer: Circumference of circle C = 3.14 xd = 3.14 x 6 = 18.84 (dm)

How much pi can be used to calculate the circumference?

According to the textbook series "Connecting knowledge with life", Math 5, in the section on rounding decimal numbers, the number π\pi is introduced as a special number, with many digits after the decimal point: "3.141592..." and requires rounding to the tenths and hundredths.

According to Math Grade 6 (Workbook - new program), the textbook explains that π\piπ is the Archimedes constant, equal to the ratio between the circumference of a circle and the diameter, with an approximate value = “3.141592653589793…” and has exercises to round this number.

Therefore, depending on the lesson requirements, you can choose the appropriate rounded pi value.

Why are the letters C, S, r, d used to indicate circle measurements?

C stands for "Circumference", S stands for "Surface area", r stands for "radius", and d stands for "diameter".

The use of these characters makes mathematical notation short, memorable, and universally accepted.

What is the formula for calculating the area of a circle? To calculate the area of a circle, the basic formula is S = rxrx π, where S is the area, r is the radius, and the constant pi π (approximately 3.14159). Additionally, if you know the circumference and diameter, you can also calculate the area of a circle.

Source: https://vietnamnet.vn/cong-thuc-tinh-chu-vi-hinh-tron-2445269.html