The circumference of the circle is 62.8 meters, the area of the circle is (), the circumference of the semicircle is 5.14 cm, and the area is ()

The circumference of the circle is 62.8 meters, the area of the circle is (), the circumference of the semicircle is 5.14 cm, and the area is ()

The perimeter of the circle is 62.8 meters, the area of the circle is (314) square meters, the perimeter of the semicircle is 5.14 cm, and the area is (1.57) square centimeters

Given the area of a circle, can we find its perimeter?
How to calculate?

Yes
Radius of circle * 2 = diameter of circle
Diameter of circle * 3.14 = circumference of circle

The circumference of a circle is 62.8. What is the area of the circle

Let the longest edge be x cm% d% ax + x-4 + X-8 = 120% d% a x = 44% d% a. the longest edge is 44 cm

The radius of the bottom of the cone is 1, and the length of the generatrix is 6. An ant starts from a point B on the circumference of the bottom, crawls along the side of the cone, and then returns to point B. what is the shortest route for it to crawl?

The radius of the bottom of a cone is 1, and the circumference of the bottom is equal to 2 π. Let the angle of the center of the fan-shaped circle be n ° after the side of the cone is expanded. According to the fact that the circumference of the bottom is equal to the arc length of the fan-shaped circle after the expansion, we get 2 π = n π × 6180, and the solution is n = 60, so the angle of the center of the circle in the expansion is 60 °. The side expansion of a cone is shown in the figure, so the shortest route length of its crawling is 6

The radius of the bottom of the cone is 1 and the length of the generatrix is 3. An ant should start from a point B on the circumference of the bottom
The radius of the bottom of the cone is 1, and the length of the generatrix is 6. An ant starts from a point B on the circumference of the bottom, climbs along the side of the cone to another generatrix AC on the axial section of generatrix AB, and asks what is the shortest route for it to crawl?
Help me, I can't understand this problem
Variant: the radius of the bottom of the cone is 1, and the length of the generatrix is 3. The ant starts from a point B on the circumference of the bottom, crawls around the side of the cone, and then returns to point B. what is the shortest route?

1. If the side of the cone is expanded into a sector, the corresponding arc length is the circumference of the bottom circle, and the corresponding chord is the shortest path. An ant should start from a point B on the circumference of the bottom circle, climb along the side of the cone to another bus AC on the axial section of the bus AB, and set the point as D,
N π * 6 / 180 = 2 π * 1, n = 60 degrees, < DAB = 30 degrees, BD = AB / 2 = 3, its shortest path is 3
2. The ant starts from a point B on the bottom circle, crawls along the side of the cone, and then returns to point B,
N π * 3 / 180 = 2 π * 1, n = 120 degrees, BB = 3 √ 3
The shortest route is 3 √ 3

If the triangle is rotated about OA, what is the volume of the cone? If the triangle is rotated about ob, what is the volume of the cone
What's the volume? (keep 2 decimal places) 8cm between a and O, 4cm between O and B, (Class 6 is really tired)
Help!

When the cone is rotated with OA as the axis for one circle, the bottom radius is ob = 4 and the height is OA = 8. The volume is 3.14 × 4 & # 178; × 8 ／ 3 = 133.97 CM & # 179; when the cone is rotated with ob as the axis for one circle, the bottom radius is OA = 8 and the height is ob = 4. The volume is 3.14 × 8 & # 178; × 4 ／ 3 = 267.95 CM & # 179

It is known that the radius of the bottom of the cone is r = 20cm and the height is 2015cm. Now an ant starts from a point a on the bottom, crawls on the side for a circle and returns to a point to find the shortest distance

Let the center angle of the sector be n, the top of the cone be e, ∵ r = 20cm, H = 2015cm. According to the Pythagorean theorem, we can get the generatrix L = R2 + H2 = 80cm, and the arc length of the expanded sector on the side of the cone is 2 × 20 π = n π × 80180, ∵ n = 90 degrees, that is, △ EAA 'is an isosceles right triangle. According to the Pythagorean theorem, we can get AA' = a 'E2 + AE2 = 802cm

A cylinder with a bottom radius of 15cm and a height of 18cm is cast into a cone with a bottom diameter of 20cm. How high is the cone

Cone radius = 20 △ 2 = 10
Cylinder volume = 3.14 × 15 × 15 × 18
Because cylinder volume = cone volume
Cone height = volume △ (1 / 3 × 3.14 × 10 × 10)
=（3.14×15×15×18）÷(1/3×3.14×10×10)
=121.5 cm

The bottom radius of the cone is 1, the height is 2 under the root sign, and the axial section is PAB?

First, unfold the side of the solid into a fan, and imagine cutting it from PA
At this time, there are two a points connected, which are the minimum length of the rope
This is the way of thinking
If the radius of high root 2 is 1, we can get | PA | = root 3
1 * 2 * pi = root 3 * 2 * pi * (A / 2pi) pi = 3.1415926, a is the fan angle
So a = pi * 2 radical 3 / 3
|AA|^2=3+3-2*3*cosa
|AA | = under root (. Same as above)

If the side view of a cone is a semicircle, the ratio of the generatrix length to the bottom radius of the cone is ()
A. 2：1B. 2π：1C. 2：1D. 3：1

If the radius of the bottom surface is R and the length of the generatrix is r, then the perimeter of the bottom surface is 2 π r = 12 × 2 π R, ∧ R: r = 2:1