Is r squared in S = (1 / 2) LR

No,
The area of a sector
Sector is an important figure related to circle. Its area is related to center angle (vertex angle) and radius of circle. The area of sector with center angle n ° and radius R is n / 360 * π R ^ 2. If the vertex angle is in radian, it can be simplified as 1 / 2 × arc length × radius. (arc length = radius × radian)
The above simplified area formula can also be regarded as: 1 / 2 × arc length × radius, which is similar to the triangle area: 1 / 2 × bottom × height
Sector area formula: s sector = (LR) / 2 (L is sector arc length)
S sector = (n / 360) π R ^ 2 (n is the degree of the center angle of the circle, R is the radius of the bottom circle)
Note: π is pi

If the circumference of a circle is increased three times, its area will be enlarged

9 times

After a circle is divided into several parts, an approximate rectangle is formed. The area of the circle is calculated. The length of the rectangle is 12.56 meters

The length of the rectangle is half of the circumference of the circle, and the radius is 12.56 △ 3.14 = 4m
Circular area: 3.14 × 4 × 4 = 50.24 square meters

3:4
Check the right and cross the wrong
1. Add 3 to the first term of 3:4, and then add 3 to the second term to keep the ratio unchanged
2. The ratio of a to B is 7:8. If B is equal to 120, a must be 105
3. A cup of salt water, salt accounts for one sixth of salt water, then the ratio of salt to water is 1:5 ()

Check the right and cross the wrong
1. Add 3 to the first term of 3:4, and then add 3 to the second term to keep the ratio unchanged
4 should be added to the latter item
2. The ratio of a to B is 7:8. If B is equal to 120, a must be 105
A is
120÷8×7＝105
3. A cup of salt water, salt accounts for one sixth of salt water, then the ratio of salt to water is 1:5 (right)
What is the ratio of salt to water
1 / 6: (1-1 / 6) = 1:5

Mathematics problems (application problems and judgment problems)
The bottom of a triangle is 10 cm, and its area is 80 cm. If its area is reduced by 20 square cm, how many cm should the bottom be shortened?
Judgment questions:
1) The book represented by - a must be negative ()
2) Of the four numbers -1.01,1.01, - 1.10, + 1.10, the smallest number is -1.01 ()
3) If any number is divided by 0.98, the quotient is greater than the divisor ()
4) 7 / 10 decimeter = 7 / 100 meter ()

If the reduced triangle and the original triangle are a pair of similar triangles, then remember that the area of the reduced triangle is S1, and the original area is s, so S1 = 60, so s: S1 = 80:60 = 4:3,
So the ratio of their bottom length is 2: √ 3
So now the triangle is 5 √ 3 long, so it should be shortened by 10-5 √ 3 cm
There is more than one answer to this question
Judgment questions
1)X 2)O 3)X 4)O

A judgment question, an application question
Judgment: in proportion, two external terms may be greater than two internal terms
According to xy = m (M is not zero), can you write a ratio?

Yes. For example, 4:3 = (- 4): (- 3)
x:m=1:y

The radius of the big circle is equal to the diameter of the small circle. It is known that the area of the big circle is 9.42 square decimeters more than that of the small circle, and the area of the small circle is______ ．

Let the radius of the small circle be r, then the radius of the big circle is 2R, the area of the big circle is: π (2R) 2 = 4 π R2, and the area of the small circle is: π R2, so the area of the big circle is 4 times of that of the small circle, then the area of the big circle is 4-1 = 3 times larger than that of the small circle, 9.42 △ 3 = 3.14 (M2). A: the area of the small circle is 3.14dm2

The radius of the big circle is equal to the diameter of the small circle. It is known that the area of the big circle is 9.42 square decimeters more than that of the small circle, and the area of the small circle is______ ．

The circumference of the rectangle is 12cm. What is the area of the semicircle? The diameter of the semicircle is equal to the length of the rectangle

Because we only know the circumference of the rectangle, we can't determine the side length of the rectangle, so we can't determine the diameter of the semicircle, so we can't calculate the area of the semicircle
If the side line of the semicircle is tangent to another long side of the rectangle, the size of the figure can be determined. If so, the radius of the semicircle can be obtained as 2; the area of the semicircle = 2x2x3.14 △ 2 = 2x3.14 = 6.28

After a circle is divided into several parts, a rectangle is formed. The perimeter of the rectangle is increased by 12 cm. The area and perimeter of the circle are calculated

According to the meaning of the title, the circumference of a rectangle is two more radii than that of a circle
Radius = 12 △ 2 = 6 (CM)
Area of circle = 3.14 × 6 × 6 = 113.04 (cm2)
Circumference of circle = 3.14 × 6 × 2 = 37.68 (CM)

Is r squared in S = (1 / 2) LR