点到二次曲线的切线

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写一个函数, 输入一点和一个二次曲线(geometry.asy定义的conic结构体), 输出点到二次曲线的所有切点?
圆的情形, 见olympiad.asy
点到圆的2个切点(按逆时针标为1和2):

1. // The nth point of tangency from a point P to the circle with center O and radius r
2. // where n can be 1 or 2 - the points of tangency are labeled in counterclockwise order around the circle.
3. // If P is inside the circle, the center of the circle is returned rather than an error.
4. pair tangent(pair P, pair O, real r, int n=1)
5. {  
6.         real d,R;  
7.         pair X,T;  
8.         d=abs(P-O);  
9.         if (d<r) return O;  
10.         R=sqrt(d^2-r^2);  
11.         X=intersectionpoint(circle(O,r),O--P);  
12.         if (n==1)
13.         {   
14.                 T=intersectionpoint(circle(P,R),Arc(O,r,degrees(X-O),degrees(X-O)+180));   
15.         }  
16.         else if (n==2)
17.         {   
18.                 T=intersectionpoint(circle(P,R),Arc(O,r,degrees(X-O)+180,degrees(X-O)+360));   
19.         }  
20.         else {T=O;}  
21.         return T;
22. }

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