1, out of circle: d >；; R 1+r2, with 0 intersections; Circumscribed: d=r 1+r2, with 1 intersections; Intersection: r 1-r2 is inscribed: d=r 1-r2, with 1 intersections; Contains: 0 ≤ d.

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

3. Square difference formula: A2-B2 = (a+b) (a-b).

4. Cubic difference formula: a3- b3=(a-b)(a2+ab+b2).

5、sin(A/2)=√(( 1-cosA)/2)sin(A/2)=-√(( 1-cosA)/2)。