7. 求矢量夹角余弦 8. 求线段之间的夹角 9. 判断线段是否相交10.判断线段是否相交但不交在端点处 11.求线段所在直线的方程 12.求直线的斜率 13.求直线的倾斜角14.求点关于某直线的对称点15.判断两条直线是否相交及求直线交点16.判断线段是否相交，如果相交返回交点-7. For vector cosine angle 8. For the angle between the line 9. Line judge whether the intersection 10. Line judge whether the intersection but do not pay the endpoint Office 11. For the straight line segment where equation 12. For a linear slope 13. Seeking straight tilt angle 14. For a certain point on a linear symmetrical 15 points. to judge whether the intersection of two straight and for 16 straight intersection. Line judge whether the intersection, the intersection to intersection