Divide a circle of 8 cm in diameter into two semicircles. What is the circumference of each semicircle?

Divide a circle of 8 cm in diameter into two semicircles. What is the circumference of each semicircle?

Yichufeng,
The circumference of the semicircle is:
3.14×8÷2＋8
＝12.56＋8
= 20.56 (CM)

He said that the circumference of a semicircle is known to be 20.56cm. The diameter of the semicircle is (arithmetically)

The circumference of a semicircle is the diameter plus half the circumference of a circle
1. Relationship between diameter (R) and circumference: circumference = π R, half circumference = π R / 2
2. Semicircle circumference = π R / 2 + diameter (R) = 3.1415r / 2 + r = 1.57r + r = 2.57r
3.2.57R=20.56
Diameter (R) = 8cm
Perimeter = π r perimeter = 2 π R

Given that the generatrix length of the cone is 30, and the center angle of the fan-shaped circle is 120 ° after the side expansion, the bottom radius of the cone is 0______ ．

Arc length = 120 π· 30180 = 20 π. According to the fact that the circumference of the bottom surface of the cone is equal to the arc length of the sector in the side view, the solution is: r = 10. The radius of the bottom surface of the cone is 10

It is known that the radius of the bottom of the cone is 5, and the center angle of the sector is 120 ° after the side is expanded, then the generatrix length of the cone is equal to______ ．

10π=120π•R180，R=15．

Given that the generatrix length of the cone is 30, and the center angle of the fan-shaped circle is 120 ° after the side expansion, the bottom radius of the cone is 0______ ．

Arc length = 120 π· 30180 = 20 π. According to the fact that the circumference of the bottom surface of the cone is equal to the arc length of the sector in the side view, the solution is: r = 10. The radius of the bottom surface of the cone is 10

It is known that the radius of the bottom of the cone is 5, and the center angle of the sector is 120 ° after the side is expanded, then the generatrix length of the cone is equal to______ ．

10π=120π•R180，R=15．

Cut a sector with a radius of 30 cm from the drawing and add a bottom surface to make a cone. The diameter of the bottom surface of the cone is 20 cm. (1) calculate the center angle of the cut sector; (2) calculate the surface area of the cone

Solution (1) the circumference of the cone bottom surface is 20 × 3.14 = 62.8 (CM), so the arc length of the sector is 62.8 cm, the circumference of the circle where the sector is located is 2 × 30 × 3.14 = 188.4 (CM), so the degree of the center angle of the sector is 62.8188.4 × 360 ° = 120 °; (2) the surface area of the sector is 3.14 × 302 × 120360 + 3

If a sector with a center angle of 288 degrees and an area of 20 π cm ^ 2 is used to form a cone, the volume of the cone is equal to

The base radius of the cone is r
The length L of conical generatrix is sector radius
The sector area is 288 / 360 * π L ^ 2 = 20 π cm ^ 2
L=5
The side area s of the cone is the area of the sector on the side of the cone=
πRL=20πcm^2
R=4
The height of the cone is h
H^2=5^2-4^2
H=3
Cone volume v = 1 / 3 (s * h) = 1 / 3 (π * R ^ 2 * h)
=16πcm^2

How does the volume of the cone enclosed by the sector with constant radius and gradually larger central angle change
The so-called radius is the edge of the sector. I don't know. I hope you can understand what I mean,

Sector arc length = R * α, base radius of cone = sector arc length / (2 π) = R * α / (2 π) base area of cone = π * base radius of Cone & sup2; = (R * α) & sup2; / (4 π) height of Cone & sup2; = R & sup2; - base radius of Cone & sup2; = R & sup2; - (R * α / (2 π)) & sup2; = R & sup2; (1 - α & sup2; / (4 π

What is the volumetric type of the vessel if the sector iron sheet with a center angle of 216 degrees and a radius of 5cm is welded into a conical vessel (excluding the weld)?
Given that the central angle of the sector is 135 degrees and the area is a, let the total area of the cone enclosed by the sector be B, and find the value of B; a

Arc length of sector = circumference of cone bottom = 216 π * 5 / 180 = 6 π
Ψ bottom radius = 3
∵ generatrix of cone = 5
The height of the cone = 4
Volume = 1 / 3 * π * 3 ^ 2 * 4 = 12 π (CC)