Derivation of the formula of the circumference of a circle (this aspect involves arc differentiation)
Let the parameter equation of a circle be.
Integral of a circle in a week
Substitute, available
Namely.
Extended data:
Formula for calculating circle area: or
Find the diameter from the area of a circle:?
Divide a circle into several equal parts and you can make an approximate rectangle. The width of a rectangle corresponds to the radius of a circle.
Transverse area of cone (L is the length of bus)
Sector arc length L= central angle (radian system) ×R= nπR/ 180(θ is central angle) (r is sector radius).
Sector area S=nπ R? /360=LR/2(L is the arc length of the sector)
Radius of cone bottom surface r=nR/360(r is the radius of bottom surface) (N is the central angle)
R is the radius of the sector, n is the degree of the central angle of the arc, π is pi, and L is the arc length corresponding to the sector. You can also divide the area of the circle where the sector is located by 360 and multiply it by the angle n of the central angle of the sector, as follows: (L is the arc length and R is the sector radius)
Deduction process: S=πr? ×L/2πr=LR/2,(L=│α│ R).
References:
Baidu encyclopedia-circle
The second volume The area of teaching reflection Chapter 65438 +0
I had a review class on the circumference and area of a circle.