Given that the area of a circle is 9 / 9 π CM & sup2;, find the circumference of the circle

Given that the area of a circle is 9 / 9 π CM & sup2;, find the circumference of the circle

S=πR^2
So π / 9 = π * R ^ 2
So r = 1 / 3
So perimeter = 2 π r = 2 π / 3

If the circumference of a circle is 314, the area of the circle is () cm

If the circumference of a circle is 3.14 times the diameter, the diameter of the circle is 100, the radius of the circle is 50, and the area of the circle is equal to 3.14 times the square of the radius, that is, 3.14 × 50 & # 178; = 7850

Given that the circumference of a circle is 6.28, how to find the area of a circle?

Perimeter = 2 π R
2πr=6.28
r=6.28/(2π)=6.28/(2*3.14)=1
Area = π (R) ^ 2 = π (1) ^ 2 = π = 3.14

If the length of the generatrix of the cone is l and the apex angle of the shaft section is a, the maximum area of the two generatrix of the cone is obtained

S = (1 / 2) · L ^ 2 · sin α. Obviously, when sin α = 1, that is, α = 90 °, s has a maximum value, which is L ^ 2 / 2

The radius of the bottom of the cone is 2cm. Make a section through two generatrix lines. The arc of the bottom is 1 / 4 of the circumference of the bottom, and the area of the section is 8cm2
Height, side area and volume

According to the result that the bottom arc is 1 / 4 of the circumference of the bottom, the center angle of the arc is 90 ° and the radius of the bottom is 2cm, so the chord length of the center angle is 2 √ 2cm. Because the section area is 8cm & # 178;, the height of the section is 8 / (2 √ 2 * 1 / 2) = 4 √ 2cm, then the generatrix is √ (4 √ 2) &# 178; + (√ 2) &# 178; = √ 3

The radius of the bottom surface of the cone is 1, the top angle of the shaft section is right angle, and the section passing through two generatrix cuts off 1 / 4 of the circumference of the bottom surface, then the section area is

Because the top angle of the shaft section is a right angle, the length of the generatrix is radical 2. Because the tangent of the bottom circle is the chord opposite to the right angle of the center of the circle, it is also radical 2, so the section is an equilateral triangle with the side length of radical 2, s = radical 3 / 2

If the angle between the generatrix and the axis of a cone is π 3 and the length of the generatrix is 3, then the center angle of the expanded side view of the cone is π 3______ Arc

The angle between generatrix and axis of the axial section of a cone is π 3, the length of generatrix is 3, the radius of the bottom circle is 3sin π 3 = 332, the perimeter of the bottom circle is 33 π, the length of generatrix is 3, and the center angle of the expanded side view of the cone is 3 π

If the side view of a cone is a semicircle with diameter a, then the axial section of the cone is ()
A. Equilateral triangle B. isosceles right triangle C. isosceles triangle with 30 ° vertex angle D. other isosceles triangle

The generatrix length of the cone is the radius of the unfolded semicircle. The arc length of the semicircle is a π, which is the circumference of the bottom surface of the cone. Therefore, the diameter of the bottom surface of the cone is a, and the axial section of the cone is an equilateral triangle

The angle between the generatrix and the height of a cone is 0______ ．

Let the generatrix length of a cone be r and the radius of its bottom be r, then: π r = 2 π R, ∧ r = 2R, ∧ the sine value of the angle between the generatrix and the height = RR = 12, ∧ the angle between the generatrix and the height is 30 °

If the side view of a cone is a semicircle with diameter a, then the axial section of the cone is ()
A. Equilateral triangle B. isosceles right triangle C. isosceles triangle with 30 ° vertex angle D. other isosceles triangle

The generatrix length of the cone is the radius of the unfolded semicircle. The arc length of the semicircle is a π, which is the circumference of the bottom surface of the cone. Therefore, the diameter of the bottom surface of the cone is a, and the axial section of the cone is an equilateral triangle