Arithmetic progression's general term formula is "an = a 1+(n-1) * d" (n: for the number of terms, d: for the tolerance, and a1:for the first term), and arithmetic progression's sum formula of the first n terms is "sn = a1. Note that n is an integer. Arithmetic progression refers to the arithmetic progression whose difference between each term and the previous term is equal to the same constant of the second term.

Area calculation formula:

1. Area of circle: S=πr? =πd？ /4

2. Sector arc length: L= central angle (arc system) * r = n π r/ 180 (n is central angle).

3. Sector area: S=nπr? /360=Lr/2(L is the chord length of the fan)

4. Diameter of circle: d=2r

5. Cone lateral area: S=πrl(l is the length of bus duct).

6. Radius of cone bottom surface: r = n/360 L (L is the length of bus duct) (R is the radius of bottom surface).

Formula derivation: circumference (c): the diameter (d) of a circle, and the circumference (c) of that circle is equal to π except the diameter (d) of the circle, so the meaning of multiplication is equal to π times the diameter (d) of the circle, and c = π d, and the diameter (d) of the same circle is twice the radius (r) of the circle, so the circumference (c) of the circle.

Dividing a circle into equal parts can spell out a similar rectangle. The width of the rectangle is equal to the radius (r) of the circle, and the length of the rectangle is half the circumference (c) of the circle. The area of the rectangle is ab, and the area of the circle is: the square meter of the radius (r) of the circle times π, and S=πr? .

The formula of circular area is: S=πr? Or S=π*(d/2)? .

Dividing the average value of a circle into equal parts can spell out a similar rectangle. The width of a rectangle is equal to the radius (r) of a circle, and the length of a rectangle is half the circumference (c). The area of the rectangle is ab, and the area of the circle is: the radius (r) of the circle times the half diameter c, and s = r * c/2 = r * π r. The related formula is also calculated as follows:

1, circular area = pi × radius× radius.

2. area of semicircle: s semicircle =(πr2) small circle 2

3. Area of semicircle = π× radius× small radius circle 2

4. Area of the circular ring: s Great Circle -s Small Circle =π(R2-r2)(R is the radius of the great circle and R is the radius of the small circle).

5. Area of circular ring = total area of outer big circle-area of inner small circle.

6, the circumference of the circle = aperture xπ.

7, semicircle circumference = π× radius+aperture