2. Number of intersections of line segments, angles and straight lines: 1/2n(n- 1).

3. The included angle of bisector of two angles of triangle: 90+ 1/2 the degree of the third angle.

4. The circumferential angle corresponding to the tangent point of two tangents of a circle = 90-65438+ 0/2 included angle of two tangents.

5. The height of hypotenuse of right triangle = ab/c.

6. The radius of the circumscribed circle of a right triangle = 1/2 hypotenuse, and the radius of the inscribed circle = 1/2(a+b-c).

7, triangle inscribed circle radius = 2sδ/ perimeter.

8, the triangle area surrounded by straight lines and coordinate axes =(b? /︱k︱)/2

9. The rectangular area surrounded by the image of the reverse function and any point of the coordinate axis =︱k︱.

10, the distance between the intersection of parabola and x axis =-x 1-x2 = √△/-a =