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本帖最后由 uk702 于 2024-1-14 16:15 编辑
改成射影几何的形式:
已知△ABC及平面上的定点 D,H,
P 是 BC 上的动点。
DP交AC于E,HP交AB于F,BE交CF于K,AB交EP于R。
AP交DH于L,EL交AB于Q,QP交AE于T,
AL交RT于M,KP交DL于G,MG交BC于N。
求证:N是定点。
代码如下:
- Clear["Global`*"];
- (*过 A、B 两点的复斜率定义*)
- k[a_, b_] := (a - b)/(a' - b');
- k'[a_, b_] := 1/k[a, b];
- (*直线 AB 与 CD 的交点*)
- FourPoint[a_, b_, c_, d_] := ((c' d - c d') (a - b) - (a' b - a b') (c - d))/((a - b) (c' - d') - (a' - b') (c - d));
- FourPoint'[a_, b_, c_, d_] := -((c d' - c' d) (a' - b') - (a b' - a' b) (c' - d'))/((a - b) (c' - d') - (a' - b') (c - d));
- b' = b = 0; c' = c = 1; p' = p = x;
- e = Simplify@FourPoint[d, p, a, c]; e' = Simplify@FourPoint'[d, p, a, c];
- f = Simplify@FourPoint[h, p, a, b]; f' = Simplify@FourPoint'[h, p, a, b];
- k = Simplify@FourPoint[b, e, c, f]; k' = Simplify@FourPoint'[b, e, c, f];
- r = Simplify@FourPoint[e, p, a, b]; r' = Simplify@FourPoint'[e, p, a, b];
- l = Simplify@FourPoint[a, p, d, h]; l' = Simplify@FourPoint'[a, p, d, h];
- q = Simplify@FourPoint[e, l, a, b]; q' = Simplify@FourPoint'[e, l, a, b];
- t = Simplify@FourPoint[q, p, a, e]; t' = Simplify@FourPoint'[q, p, a, e];
- m = Simplify@FourPoint[a, l, r, t]; m' = Simplify@FourPoint'[a, l, r, t];
- g = Simplify@FourPoint[p, k, d, l]; g' = Simplify@FourPoint'[p, k, d, l];
- n = Simplify@FourPoint[m, g, b, c]; n' = Simplify@FourPoint'[m, g, b, c];
- (* 验证 n 的坐标与 x 无关 *)
- Print["n = ", n}
复制代码
输出:
\( n =\frac{ \left(a' \left(h d'+d \left(h'-2 h\right)\right)+a \left(d' \left(h-2 h'\right)+d h'\right)\right)}{a' \left(d'-d+h'-h\right)-d' \left(a+2 h'-2 h\right)+a d-a h'+a h+2 d h'-2 d h} \)
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