|
楼主 |
发表于 2018-7-26 08:19
|
显示全部楼层
本帖最后由 天山草@ 于 2018-7-27 10:26 编辑
在【数学研发论坛】上,有人给出了下述结果:
设 x, y, z 是已知的角平分线长,那么边长 a, b, c 中的 a 是方程 f(a,x,y,z)=0 的一个正实数根。f 的表达式如下:
f = 256 a^20 (x - y)^2 y^2 (x + y)^2 (x - z)^2 z^2 (x + z)^2 (x y -
x z - y z) (x y + x z - y z) (x y - x z + y z) (x y + x z +
y z) + 256 a^18 (x^14 y^8 - 2 x^12 y^10 + x^10 y^12 -
9 x^12 y^8 z^2 + 11 x^10 y^10 z^2 - 6 x^8 y^12 z^2 -
2 x^14 y^4 z^4 + 3 x^12 y^6 z^4 + 40 x^10 y^8 z^4 -
31 x^8 y^10 z^4 + 14 x^6 y^12 z^4 + 3 x^12 y^4 z^6 -
x^10 y^6 z^6 - 66 x^8 y^8 z^6 + 44 x^6 y^10 z^6 -
16 x^4 y^12 z^6 + x^14 z^8 - 9 x^12 y^2 z^8 + 40 x^10 y^4 z^8 -
66 x^8 y^6 z^8 + 72 x^6 y^8 z^8 - 31 x^4 y^10 z^8 +
9 x^2 y^12 z^8 - 2 x^12 z^10 + 11 x^10 y^2 z^10 -
31 x^8 y^4 z^10 + 44 x^6 y^6 z^10 - 31 x^4 y^8 z^10 +
11 x^2 y^10 z^10 - 2 y^12 z^10 + x^10 z^12 - 6 x^8 y^2 z^12 +
14 x^6 y^4 z^12 - 16 x^4 y^6 z^12 + 9 x^2 y^8 z^12 -
2 y^10 z^12) -
32 a^16 (40 x^14 y^10 - 24 x^12 y^12 + 16 x^10 y^14 +
40 x^14 y^8 z^2 - 299 x^12 y^10 z^2 + 137 x^10 y^12 z^2 -
72 x^8 y^14 z^2 - 80 x^14 y^6 z^4 - 320 x^12 y^8 z^4 +
795 x^10 y^10 z^4 - 351 x^8 y^12 z^4 + 128 x^6 y^14 z^4 -
80 x^14 y^4 z^6 + 166 x^12 y^6 z^6 + 971 x^10 y^8 z^6 -
1097 x^8 y^10 z^6 + 390 x^6 y^12 z^6 - 112 x^4 y^14 z^6 +
40 x^14 y^2 z^8 - 320 x^12 y^4 z^8 + 971 x^10 y^6 z^8 -
1155 x^8 y^8 z^8 + 762 x^6 y^10 z^8 - 178 x^4 y^12 z^8 +
48 x^2 y^14 z^8 + 40 x^14 z^10 - 299 x^12 y^2 z^10 +
795 x^10 y^4 z^10 - 1097 x^8 y^6 z^10 + 762 x^6 y^8 z^10 -
274 x^4 y^10 z^10 + 49 x^2 y^12 z^10 - 8 y^14 z^10 -
24 x^12 z^12 + 137 x^10 y^2 z^12 - 351 x^8 y^4 z^12 +
390 x^6 y^6 z^12 - 178 x^4 y^8 z^12 + 49 x^2 y^10 z^12 -
23 y^12 z^12 + 16 x^10 z^14 - 72 x^8 y^2 z^14 +
128 x^6 y^4 z^14 - 112 x^4 y^6 z^14 + 48 x^2 y^8 z^14 -
8 y^10 z^14) +
16 a^14 (118 x^14 y^12 - 2 x^12 y^14 + 16 x^10 y^16 +
428 x^14 y^10 z^2 - 807 x^12 y^12 z^2 + 172 x^10 y^14 z^2 -
64 x^8 y^16 z^2 - 118 x^14 y^8 z^4 - 2001 x^12 y^10 z^4 +
1542 x^10 y^12 z^4 - 398 x^8 y^14 z^4 + 96 x^6 y^16 z^4 -
856 x^14 y^6 z^6 - 1022 x^12 y^8 z^6 + 3120 x^10 y^10 z^6 -
1772 x^8 y^12 z^6 + 280 x^6 y^14 z^6 - 64 x^4 y^16 z^6 -
118 x^14 y^4 z^8 - 1022 x^12 y^6 z^8 + 3533 x^10 y^8 z^8 -
2347 x^8 y^10 z^8 + 817 x^6 y^12 z^8 - 62 x^4 y^14 z^8 +
16 x^2 y^16 z^8 + 428 x^14 y^2 z^10 - 2001 x^12 y^4 z^10 +
3120 x^10 y^6 z^10 - 2347 x^8 y^8 z^10 + 1040 x^6 y^10 z^10 -
365 x^4 y^12 z^10 + 28 x^2 y^14 z^10 + 118 x^14 z^12 -
807 x^12 y^2 z^12 + 1542 x^10 y^4 z^12 - 1772 x^8 y^6 z^12 +
817 x^6 y^8 z^12 - 365 x^4 y^10 z^12 - 87 x^2 y^12 z^12 -
18 y^14 z^12 - 2 x^12 z^14 + 172 x^10 y^2 z^14 -
398 x^8 y^4 z^14 + 280 x^6 y^6 z^14 - 62 x^4 y^8 z^14 +
28 x^2 y^10 z^14 - 18 y^12 z^14 + 16 x^10 z^16 -
64 x^8 y^2 z^16 + 96 x^6 y^4 z^16 - 64 x^4 y^6 z^16 +
16 x^2 y^8 z^16) -
a^12 (720 x^14 y^14 + 288 x^12 y^16 + 10608 x^14 y^12 z^2 -
3217 x^12 y^14 z^2 + 288 x^10 y^16 z^2 + 11216 x^14 y^10 z^4 -
35778 x^12 y^12 z^4 + 8666 x^10 y^14 z^4 - 576 x^8 y^16 z^4 -
22544 x^14 y^8 z^6 - 43775 x^12 y^10 z^6 +
18872 x^10 y^12 z^6 - 5967 x^8 y^14 z^6 - 576 x^6 y^16 z^6 -
22544 x^14 y^6 z^8 - 37340 x^12 y^8 z^8 + 34894 x^10 y^10 z^8 -
20854 x^8 y^12 z^8 + 2140 x^6 y^14 z^8 + 288 x^4 y^16 z^8 +
11216 x^14 y^4 z^10 - 43775 x^12 y^6 z^10 +
34894 x^10 y^8 z^10 - 19615 x^8 y^10 z^10 -
3050 x^6 y^12 z^10 - 143 x^4 y^14 z^10 + 288 x^2 y^16 z^10 +
10608 x^14 y^2 z^12 - 35778 x^12 y^4 z^12 +
18872 x^10 y^6 z^12 - 20854 x^8 y^8 z^12 - 3050 x^6 y^10 z^12 -
6480 x^4 y^12 z^12 - 966 x^2 y^14 z^12 + 720 x^14 z^14 -
3217 x^12 y^2 z^14 + 8666 x^10 y^4 z^14 - 5967 x^8 y^6 z^14 +
2140 x^6 y^8 z^14 - 143 x^4 y^10 z^14 - 966 x^2 y^12 z^14 -
81 y^14 z^14 + 288 x^12 z^16 + 288 x^10 y^2 z^16 -
576 x^8 y^4 z^16 - 576 x^6 y^6 z^16 + 288 x^4 y^8 z^16 +
288 x^2 y^10 z^16) +
a^10 x^2 (81 x^12 y^16 + 3972 x^12 y^14 z^2 + 1254 x^10 y^16 z^2 +
22468 x^12 y^12 z^4 - 8012 x^10 y^14 z^4 + 1215 x^8 y^16 z^4 -
3972 x^12 y^10 z^6 - 34520 x^10 y^12 z^6 + 1672 x^8 y^14 z^6 +
84 x^6 y^16 z^6 - 45098 x^12 y^8 z^8 - 35778 x^10 y^10 z^8 -
11013 x^8 y^12 z^8 - 2152 x^6 y^14 z^8 + 1215 x^4 y^16 z^8 -
3972 x^12 y^6 z^10 - 35778 x^10 y^8 z^10 - 4764 x^8 y^10 z^10 -
10400 x^6 y^12 z^10 - 860 x^4 y^14 z^10 + 1254 x^2 y^16 z^10 +
22468 x^12 y^4 z^12 - 34520 x^10 y^6 z^12 -
11013 x^8 y^8 z^12 - 10400 x^6 y^10 z^12 -
12772 x^4 y^12 z^12 - 1868 x^2 y^14 z^12 + 81 y^16 z^12 +
3972 x^12 y^2 z^14 - 8012 x^10 y^4 z^14 + 1672 x^8 y^6 z^14 -
2152 x^6 y^8 z^14 - 860 x^4 y^10 z^14 - 1868 x^2 y^12 z^14 -
432 y^14 z^14 + 81 x^12 z^16 + 1254 x^10 y^2 z^16 +
1215 x^8 y^4 z^16 + 84 x^6 y^6 z^16 + 1215 x^4 y^8 z^16 +
1254 x^2 y^10 z^16 + 81 y^12 z^16) -
a^8 x^4 y^2 z^2 (432 x^10 y^14 + 8336 x^10 y^12 z^2 +
2672 x^8 y^14 z^2 + 19760 x^10 y^10 z^4 - 4049 x^8 y^12 z^4 +
3808 x^6 y^14 z^4 - 28528 x^10 y^8 z^6 - 11252 x^8 y^10 z^6 -
3748 x^6 y^12 z^6 + 3808 x^4 y^14 z^6 - 28528 x^10 y^6 z^8 -
4966 x^8 y^8 z^8 - 17532 x^6 y^10 z^8 + 442 x^4 y^12 z^8 +
2672 x^2 y^14 z^8 + 19760 x^10 y^4 z^10 - 11252 x^8 y^6 z^10 -
17532 x^6 y^8 z^10 - 9980 x^4 y^10 z^10 - 2740 x^2 y^12 z^10 +
432 y^14 z^10 + 8336 x^10 y^2 z^12 - 4049 x^8 y^4 z^12 -
3748 x^6 y^6 z^12 + 442 x^4 y^8 z^12 - 2740 x^2 y^10 z^12 -
945 y^12 z^12 + 432 x^10 z^14 + 2672 x^8 y^2 z^14 +
3808 x^6 y^4 z^14 + 3808 x^4 y^6 z^14 + 2672 x^2 y^8 z^14 +
432 y^10 z^14) +
16 a^6 x^6 y^4 z^4 (54 x^8 y^12 + 492 x^8 y^10 z^2 +
216 x^6 y^12 z^2 + 202 x^8 y^8 z^4 + 121 x^6 y^10 z^4 +
324 x^4 y^12 z^4 - 1496 x^8 y^6 z^6 + 235 x^6 y^8 z^6 +
3 x^4 y^10 z^6 + 216 x^2 y^12 z^6 + 202 x^8 y^4 z^8 +
235 x^6 y^6 z^8 - 368 x^4 y^8 z^8 - 149 x^2 y^10 z^8 +
54 y^12 z^8 + 492 x^8 y^2 z^10 + 121 x^6 y^4 z^10 +
3 x^4 y^6 z^10 - 149 x^2 y^8 z^10 - 75 y^10 z^10 +
54 x^8 z^12 + 216 x^6 y^2 z^12 + 324 x^4 y^4 z^12 +
216 x^2 y^6 z^12 + 54 y^8 z^12) -
32 a^4 x^8 y^6 z^6 (24 x^6 y^10 + 88 x^6 y^8 z^2 +
72 x^4 y^10 z^2 - 112 x^6 y^6 z^4 + 29 x^4 y^8 z^4 +
72 x^2 y^10 z^4 - 112 x^6 y^4 z^6 + 10 x^4 y^6 z^6 -
46 x^2 y^8 z^6 + 24 y^10 z^6 + 88 x^6 y^2 z^8 +
29 x^4 y^4 z^8 - 46 x^2 y^6 z^8 - 35 y^8 z^8 + 24 x^6 z^10 +
72 x^4 y^2 z^10 + 72 x^2 y^4 z^10 + 24 y^6 z^10) +
256 a^2 x^10 y^8 z^8 (x^2 y^2 + x^2 z^2 + y^2 z^2) (x^2 y^6 -
x^2 y^4 z^2 + y^6 z^2 - x^2 y^2 z^4 - 3 y^4 z^4 + x^2 z^6 +
y^2 z^6) + 256 x^12 y^14 z^14;
从上面这方程求解 a 的表达式(还需要加上一些条件),即使能解出来,结果也必定是极其复杂的和不优美的!况且,次数大于等于 5 次的一般代数方程是没有根式解的。上面这个 20 次方程估计也不会有。
|
|