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What is the summary of mathematical formulas in the first volume of the ninth grade?
The mathematical formula of the first volume of the ninth grade is summarized as follows:

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)。