![](https://cache.ptt.cc/c/https/i.imgur.com/sOvPdVml.jpg?e=1718857485&s=MMf2uj1GmynR9ZFmVAiv3w)
※ 引述《maybe85912 (英雄不流淚)》之銘言:
: http://i.imgur.com/sOvPdVm.jpg
: 角XOY為40度
: P點為角XOY內任意點
: 做一點A於線段OX上,點B於線段OY上
: 求當三角形APB周長最小時,
: 角APB為幾度?
P對OX的對稱點P'
P對OY的對稱點P"
P'P"分別交OX與OY於A, B二點
∠P'PP" = 180 - 40
= 140
= 180 - ∠PP'P" - ∠PP"P'
=> ∠APB = 180 - 2[∠PP'P" + ∠PP"P']
= 180 - 80
= 100度
--
※ 發信站: 批踢踢實業坊(ptt.cc), 來自: 111.249.191.231
※ 文章網址: https://www.ptt.cc/bbs/Math/M.1488552972.A.59B.html
![](https://cache.ptt.cc/c/https/i.imgur.com/sOvPdVml.jpg?e=1718857485&s=MMf2uj1GmynR9ZFmVAiv3w)