欧拉计划 发表于 2017-1-13 15:16:54

题目257:角平分线

Angular Bisectors

Given is an integer sided triangle ABC with sides a ≤ b ≤ c. (AB = c, BC = a and AC = b).
The angular bisectors of the triangle intersect the sides at points E, F and G (see picture below).



The segments EF, EG and FG partition the triangle ABC into four smaller triangles: AEG, BFE, CGF and EFG.
It can be proven that for each of these four triangles the ratio area(ABC)/area(subtriangle) is rational.
However, there exist triangles for which some or all of these ratios are integral.

How many triangles ABC with perimeter≤100,000,000 exist so that the ratio area(ABC)/area(AEG) is integral?

题目:

下图给定一个边为 a ≤ b ≤ c 的整边三角形ABC。(AB = c,BC = a,AC = b)。
三角形的角平分线分别交边于点 E,F,G (见下图)。



线段 EF,EG,FG 将三角形 ABC 分割成 4 个小三角形:AEG,BFE,CGF 和 EFG。
可以证明对于这 4 个三角形中的任何一个,ABC 的面积/小三角形的面积的比值为有理数。
然而,存在三角形使得一些或者所有比值为整数。

存在多少周长 ≤ 100,000,000 的三角形ABC,使得比值 ABC 的面积/AEG 的面积为整数?


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