2. Calculation formula of arc length: L = nχr/ 180.

3. Sector area formula: s sector =n r 2/360 = LR/2.

5. Inner common tangent length =d-(R-r) Outer common tangent length =d-(R+r)

6.① Two circles are circumscribed by D > R+R ② Two circles are circumscribed by d=R+r③ Two circles intersect R-R < D < R+R (R > R) ④ Two circles are inscribed by D = R-R (R > R) ⑤ Two circles contain D < R-R (R > R).

7. Theorem The intersection line of two circles bisects the common chord of two circles vertically.

8. Theorem divides a circle into n (n ≥ 3): ⑴ The polygon obtained by connecting points in turn is an inscribed regular N polygon of the circle ⑴ The polygon whose vertices are the intersection of adjacent tangents is an circumscribed regular N polygon of the circle.

9. Theorem Any regular polygon has a circumscribed circle and an inscribed circle, which are concentric circles.

10. If there are k positive n corners around a vertex, since the sum of these corners should be 360, then K× (n-2) 180/n = 360 becomes (n-2)(k-2)=4.

1 1, formula: a3+B3+C3-3abc = (a+b+c) (a2+B2+C2-ab-BC-ca).

12, square difference formula: a square -b square =(a+b)(a-b)

13, complete square sum formula: (a+b) square =a square +2ab+b square.

14, complete square difference formula: (a-b) square =a square -2ab+b square.

15, two formulas: ax 2+bx+c = a [x-(-b+√ (B2-4ac))/2a] [x-(-b-√ (B2-4ac))/2a]

15, cubic sum formula: A 3+B 3 = (A+B) (A 2-AB+B 2)

16, cubic difference formula: A 3-B 3 = (A-B) (A 2+AB+B 2)

17, complete cubic formula: A 3 3a 2b+3ab 2 b 3 = (A b) 3 Solution of a quadratic equation with one variable -b+√(b2-4ac)/2a -b-√(b2-4ac)/2a.

18, the relationship between root and coefficient x1+x2 =-b/ax1* x2 = c/a Note: Vieta's theorem.

19, discriminant b2-4ac=0 Note: the equation has two equal real roots B2-4ac >；; 0 Note: This equation has two unequal real roots B2-4ac.

20 、| a+b |≤| a |+| b | | a-b |≤| a |+| b | | a |≤b & lt； = & gt-b≤a≤b |a-b|≥|a|-|b|-|a|≤a≤|a|

2 1, the sum of the first n terms of some sequences1+2+3+4+5+6+7+8+9+…+n = n (n+1)/21+3+5+7+.

22、2+4+6+8+ 10+ 12+ 14+…+(2n)= n(n+ 1) 12+22+32+42+52+72+82+…+N2 = n(n+ 1)(2n+ 1)/6 13+23+33

23. The sum formula of the two angles is SIN (A+B) = Sina COSB+COSA SINB SIN (A-B) = Sina COSB-SINB COSA.

24. The sum formula of two angles COS (a+b) = COSA COSB-SINA SINB COS (a-b) = COSA COSB+SINA SINB.

24. The sum of the two angles is tan (a+b) = (tana+tanb)/(kloc-0/-tanatanb) tan (a-b) = (tanatanb)/(kloc-0/+tanatanb).

25、ctg(A+B)=(ctgActgB- 1)/(ctg B+ctgA)ctg(A-B)=(ctgActgB+ 1)/(ctg B-ctgA)

26. The angle doubling formula tan2a = 2tana/(1-tan2a) ctg2a = (ctg2a-1)/2ctga cos2a = cos2a-sin2a = 2cos2a-1=1-2sin2a.

27. the half-angle formula sin (a/2) = √ ((1-COSA)/2) sin (a/2) =-√ ((1-COSA)/2).

28. Half-angle formula COS (a/2) = √ ((kloc-0/+COSA)/2) COS (a/2) =-√ ((kloc-0/+COSA)/2).

29. Half-angle formula Tan (a/2) = √ (1-COSA)/(1+COSA)) Tan (a/2) =-√ (1+).

30、ctg(A/2)=√(( 1+cosA)/(( 1-cosA))ctg(A/2)=-√(( 1+cosA)/(( 1-cosA))

3 1, sum product 2 Sinar COSB = symplectic (A+B)+ symplectic (A-B)2 Coxsacin B = symplectic (A+B)- symplectic (A-B)

3 1、2 cosa cosb = cos(A+B)-sin(A-B)-2 sinasinb = cos(A+B)-cos(A-B)

32、sinA+sinB = 2 sin((A+B)/2)cos((A-B)/2 cosa+cosB = 2 cos((A+B)/2)sin((A-B)/2)

33、tanA+tanB = sin(A+B)/cosAcosBtanA-tanB = sin(A-B)/cosAcos

34、ctgA+ctgBsin(A+B)/Sina sin B-ctgA+ctgBsin(A+B)/Sina sinb