The radius of the small circle is a, the radius of the large circle is B, and the perimeter ratio of the large and small circles is? Area ratio "?

The radius of the small circle is a, the radius of the large circle is B, and the perimeter ratio of the large and small circles is? Area ratio "?

The radius of the small circle is a, the radius of the large circle is B, and the perimeter ratio of the large and small circles is a: B
The area ratio is a-178; b-178;

If the radius of the big circle is twice that of the small circle, then the area of the big circle is (),
And the area of the little circle

Let the radius of the small circle be r cm
3.14(4r+2r)=28.26
3.14*6r=28.26
R = 28.26 / (3.14 * 6) = 1.5cm
Large circle area: 3.14 * (2R) ^ 2 = 3.14 * (2 * 1.5) ^ 2 = 28.26 square centimeter
Small circle area: 3.14 * (1.5 ^ 2) = 7.065 square centimeters

The radius of the small circle is 13 times that of the large circle, and the perimeter ratio of the small circle to the large circle is______ And the area ratio is______ ．

Suppose the radius of the big circle is r, then the radius of the small circle is 13R, the perimeter of the small circle is 2 π 13R, the perimeter of the big circle is 2 π R, their ratio is 2 π 13R: 2 π r = 13:1 = 1:3; the area ratio is 2 π (13R) 2:2 π R2 = 19:1 = 1:9; so the answer is 1:3, 1:9

The surface area of a cone is a square meter, and its side view is a semicircle. Find the volume of the cone

Let the radius of the bottom be r, then the perimeter of the bottom be 2 π R, and expand into a semicircle, then the radius of the semicircle (that is, the length of the generatrix) is 2R, and the height is h, H & sup2; = (2R) & sup2; - R & sup2;, H = √ 3R, so the volume of the cone is 1 / 3 π R & sup2; × √ 3R = √ 3 / 3 π R & sup3;

If the side area of a cone is three times of the bottom area, then the degree of the center angle of the expanded side view of the cone is ()
A. 180°B. 120°C. 90°D. 60°

Let the radius of the bottom circle be r, the radius of the side expanded sector be r, and the angle of the center of the sector be n degrees

A cone-shaped paper cup used to make ice cream is cut along the generatrix, and a fan-shaped cup with a radius of 20cm and a central angle of 216 ° is obtained,
Find the bottom radius and height of the paper cup

The perimeter of the bottom surface is 216 / 360 * 2 * 20 π = 24 π cm
The bottom radius is 24 π / (2 π) = 12cm
The height is equal to (20 ^ 2-12 ^ 2) ^ 1 / 2 = 9cm

The bottom circumference of the cone is 36, the generatrix is 8, and the area of the cone is calculated

If the circumference of the bottom surface of the cone is 36, then the radius of the bottom surface of the cone is 36 / 2 π = 18 / π
Base area of cone = π * (18 / π) ^ 2 = 324 / π
Side area of cone = area of expanded sector of cone = π * 8 * 8 * 36 / (2 π * 8) = 144
Surface area of cone = bottom area of cone + side area of cone = (324 / π) + 144 = 247.18

Is the side area of the cone bottom perimeter × generatrix △ 2?

Yes
S = (1 / 2) × sector radius × sector arc length
= （1/2）× L × （2πR）
= π R L
Sector radius -- bus length L
Sector arc length - bottom circumference

If the circumference of the bottom surface of a cone is 32 cm and the length of the generatrix is 7 cm, then the side area of the cone is 0______ ．

The side area of the cone is 12 × 32 × 7 = 112 cm2

If the side area of the cone is 6 pie [3.141592654], and the perimeter of the bottom surface is 2 pie, the length of the generatrix is 2 pie

1/2ar^2=6π
2πr=2π
A = 12 π r = 1
Bus L = ar = 12 π