The area ratio of circle a and circle B is 4:9. The perimeter of circle a is 25.12 decimeters. What are the perimeter and area of circle B

The area ratio of circle a and circle B is 4:9, so the perimeter of circle a: the perimeter of circle B = 2:3
Circumference of circle B = 25.12 △ 2 × 3 = 37.68 (decimeter)
Radius of circle B = 37.68 △ 3.14 △ 2 = 6 (decimeter)
Area of circle B = 3.14 × 6 × 6 = 113.04 (square decimeter)

A cone, from the front of a triangle, the bottom is 4cm, the height is 1cm

3.14 * (4 / 2) square * 1 * 1 / 3
＝4/3π

The length of the generatrix of the cone is 1, the angle of the center of the circle in the side view is 240 ° and the volume of the cone is ()
A. 22π81B. 8π81C. 45π81D. 10π81

The arc length of the side expanded view is the circumference of the bottom surface of the cone: 4 π 3, the radius of the bottom surface: 23, the height: 53, and the volume of the cone: 13 × π× (23) 2 × 53 = 45 π 81, so C is selected

For a sector cone with an area of 3 π and a center angle of 120 degrees, the surface area and volume of the cone are calculated

It's simple, but there are many steps
1. The sector area is 3 π. Sector area S1 = π * r * r * (120 / 360) = 3 π
The radius of the sector is r = 3
2. The arc length of the sector is L = π * 2R * (120 / 360) = 2 π
3. The circle length of the bottom surface of a cone rolled by a fan is a fan, and the arc length is 2 π
Let the radius of the base of a cone be r, and the equation is 2 π r = 2 π
Then: r = 1
4. If the side length of the cone is 3 and the bottom radius is 1, the height h of the cone is 2 √ 2 (2 root sign 2)
5. The surface area of a cone is the area of the bottom circle plus the side area (sector area): π * r * r + 3 π = 4 π
6. The volume is 1 / 3 * (π * r * r * h) = 1 / 3 * 2 √ 2 π

If the side area of a cone is twice of the bottom area, then the degree of the center angle of the sector in the side expanded view of the cone is______ Degree

Let R be the length of generatrix, R be the radius of the bottom, R be the perimeter of the bottom, R be the area of the bottom, R be the area of the side, R be the area of the side, R be the area of the bottom, R be the radius of the bottom, R be the radius of the bottom, R be the perimeter of the bottom, R be the perimeter of the bottom, R be the area of the bottom, R be the area of the side, R be the area of the side, R be the area of the side, R be the radius of the bottom, R be the radius of the bottom, R be the radius of the bottom, R be the radius of the bottom

If the side area of a cone is twice of the bottom area, then the degree of the center angle of the sector in the side expanded view of the cone is______ Degree

It is known that the expanded drawing of a cone is semicircle and height. How to calculate the side area

Cone area is expanded into a sector, radius is generatrix length, and sector angle is 360 * bottom radius / generatrix length

The height of a cone is 10 cm, and the expanded drawing of the rubbing surface is a semicircle

Let a be the radius of the bottom edge, B be the radius of the semicircle of the side expansion, and a ^ 2 + 10 ^ 2 = B ^ 2; (Pythagorean theorem)
Because it is a semicircle, the arc length = the circumference of the bottom surface, that is, π B = 2 π a, B = 2A;
So a = 10 / radical 3, B = 20 / radical 3;
Side area = 0.5 * π B ^ 2 = 209.3 cm2

Here is an expanded view of a cone. Can you find its side area and bottom radius?
The bus length is 6cm and the degree is 120 degrees,

Side area = 120 °△ 360 °× π × 6 × 6 = 18 π (cm2)
The bottom radius is r
1/3×π·2×6=2πr
r=2cm

When the side area of a cone is 32, the volume of the cone is 1

The side unfolded semicircle has an area of 32 π
(π * r * r) / 2 = 32 * π, r = 8, that is, the side edge of the cone is 8
That is to say, the radius of the side unfolded semicircle is 8. In the side unfolded semicircle, the arc length = (2 * π * r) / 2 = 8 π
This arc length is the circumference of the cone bottom circle. In the cone bottom circle, if the circumference = 2 * π * r = 8 π, then r = 4, that is, the cone bottom radius is 4
The area of the bottom circle is π * 4 * 4 = 16 π
The side edge of the cone is 8, the bottom radius of the cone is 4, and the height of the cone is 4 √ 3
So cone volume = (1 / 3) * s bottom * H = (1 / 3) * 16 π * 4 √ 3 = (64 √ 3 π) / 3 ≈ 116

The area ratio of circle a and circle B is 4:9. The perimeter of circle a is 25.12 decimeters. What are the perimeter and area of circle B