The proof of the formula of sector area! Let a sector radius be r and arc length be l, then the sector area s = 1 / 2lr. Why? Proof of the formula of sector area! Let a sector radius be r and arc length be l, then the sector area s = 1 / 2lr. Why? Proof!

The proof of the formula of sector area! Let a sector radius be r and arc length be l, then the sector area s = 1 / 2lr. Why? Proof of the formula of sector area! Let a sector radius be r and arc length be l, then the sector area s = 1 / 2lr. Why? Proof!

For a sector, let the center angle of a sector be n ° and its radius be r. let its arc length be L. first, we investigate the relationship between its arc length L and the circumference C of the circle. The center angle of the circle opposite the circle is 360 ° and its length is 2 π R. The arc length of the sector is L = (360 ° / N °) × (2 π R); (1 / 2) l = (360 ° / N °

Derivation of sector area formula s = 0.5 * L * R ^ 2
How does s = 1 / 2 × L × r come from

Let the sector arc be α
Then s = α / 2 π × π R ^ 2 = 1 / 2 × α R × r = 1 / 2 × L × R

What is the sector area formula s = π R & # 178; × L / 2 π r = LR / 2 π R & # 178; and what is L / 2 π r?

π R ^ 2 is the area of a complete circle
L / 2 π r refers to the ratio of the arc length L of the sector to the circumference 2 π R, that is, the ratio of the area
So s = π R ^ 2 * L / 2 π R means that the s sector occupies so many parts of L / 2 π r of the complete s circle

The diameter of a small circle is one third of the diameter of a large circle. The perimeter ratio of the small circle to the large circle is () and the area ratio of the small circle to the large circle is

The diameter of a small circle is one third of that of a large circle. The perimeter ratio of the small circle to the large circle is (1:3) and the area ratio of the small circle to the large circle is 1:9

The radius of the big circle is equal to the diameter of the small circle, and the circumference ratio of the big circle to the small circle is______ What is the area ratio of the big circle to the small circle______ A.2：1   B.1：2   C.1：4   D.4：1．

Let the radius of the small circle be r, then the diameter of the small circle be 2R, and the radius of the large circle be 2R, then: (1) [2 × π× (2R)]: (2 π R), = 4 π R: 2 π R, = 2:1; (2) π (2R) 2: π R2, = 4 π R2: π R2, = 4:1; answer: the ratio of the circumference of the large circle to the circumference of the small circle is 2:1, and the ratio of the surface product of the large circle to the area of the small circle is 4:1

If the circumference of the circle is reduced to 12, the area of the circle will be the same______ ．

The original circle perimeter = 2 π R, area = π R2, reduced circle perimeter = 2 π R × 12 = π R, reduced circle radius = π R △ 2 π = R2, reduced circle area = π (R2) 2, π (R2) 2 △ π R2, = 14; so the answer is: 14

() is called the circumference of a circle. () is called the area of a circle
() is called the circumference of a circle. () is called the area of a circle. A circle can be divided into several parts along its radius to form an approximate rectangle whose length is equal to ()

The concept in the book

Is the circumference of a circle equal to its area

Unequal
The formulas are: circle = 2 π R, circle area = π R & # 178;
One is for length and the other is for area

The sum of the circumference, diameter and radius of a circle is 9.28 cm. The diameter of the circle is______ Cm, the area is______ Square centimeter

The diameter of the circle is 1 × 2 = 2 (CM), and the area of the circle is 3.14 × 12 = 3.14 (CM). A: the diameter of the circle is 2 cm, and the area is 3.14 square cm

The circumference of a semicircle is 10.28cm. What's its radius

Suppose that π is about 3.14, then 10.28 divided by 3.14 is about 3.27cm, so the answer is 3.27cm