【阅读材料】平面几何中的费马问题是十七世纪法国数学家皮埃尔
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmo%3E%E2%8B%85%3C%2Fmo%3E%3C%2Fmath%3E)
德
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmo%3E%E2%8B%85%3C%2Fmo%3E%3C%2Fmath%3E)
费马提出的一个著名的几何问题:给定不在一条直线上的三个点
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3EA%3C%2Fmtext%3E%3C%2Fmath%3E)
、
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3EB%3C%2Fmtext%3E%3C%2Fmath%3E)
、
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3EC%3C%2Fmtext%3E%3C%2Fmath%3E)
, 求平面上到这三个点的距离之和最短的点
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3EP%3C%2Fmtext%3E%3C%2Fmath%3E)
的位置,费马问题有多种不同的解法,最简单快捷的还是几何解法
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmn%3E.%3C%2Fmn%3E%3C%2Fmath%3E)
如图1,我们可以将
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3E%E2%96%B3%3C%2Fmtext%3E%3Cmtext%3EB%3C%2Fmtext%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3EC%3C%2Fmtext%3E%3C%2Fmath%3E)
绕点
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3EB%3C%2Fmtext%3E%3C%2Fmath%3E)
顺时针旋转
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmn%3E6%3C%2Fmn%3E%3Cmn%3E0%3C%2Fmn%3E%3Cmo%3E%C2%B0%3C%2Fmo%3E%3C%2Fmath%3E)
得到
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3E%E2%96%B3%3C%2Fmtext%3E%3Cmtext%3EB%3C%2Fmtext%3E%3Cmtext%3ED%3C%2Fmtext%3E%3Cmtext%3EE%3C%2Fmtext%3E%3C%2Fmath%3E)
, 连接
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3ED%3C%2Fmtext%3E%3C%2Fmath%3E)
, 可得
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3E%E2%96%B3%3C%2Fmtext%3E%3Cmtext%3EB%3C%2Fmtext%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3ED%3C%2Fmtext%3E%3C%2Fmath%3E)
为等边三角形,故
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3ED%3C%2Fmtext%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3EB%3C%2Fmtext%3E%3C%2Fmath%3E)
, 由旋转可得
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3ED%3C%2Fmtext%3E%3Cmtext%3EE%3C%2Fmtext%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3EC%3C%2Fmtext%3E%3C%2Fmath%3E)
, 因
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3EA%3C%2Fmtext%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3EB%3C%2Fmtext%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3EC%3C%2Fmtext%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3EA%3C%2Fmtext%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3ED%3C%2Fmtext%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmtext%3ED%3C%2Fmtext%3E%3Cmtext%3EE%3C%2Fmtext%3E%3C%2Fmath%3E)
, 由两点之间线段最短可知,
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3EA%3C%2Fmtext%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3EB%3C%2Fmtext%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmtext%3EP%3C%2Fmtext%3E%3Cmtext%3EC%3C%2Fmtext%3E%3C%2Fmath%3E)
的最小值与线段
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmtext%3EA%3C%2Fmtext%3E%3Cmtext%3EE%3C%2Fmtext%3E%3C%2Fmath%3E)
的长度相等.
【解决问题】如图2,在直角三角形
内部有一动点
,
,
, 连接
,
,
, 若
, 求
的最小值 .
![](http://tikupic.21cnjy.com/2023/05/15/f1/e8/f1e8cda2478a42a92c042bde1c368838.png)