AREA唔明
2007-04-09 11:36 am
回答 (1)
2007-04-09 6:42 pm
✔ 最佳答案
圖片參考：http://homelf.kimo.com.tw/o_ohm_o/yy.JPG
BD = √(a^2 + a^2)
BD = (√2)a
BF = BD = (√2)a
∠BCE = 45˚ (main point)
by sin law
BC / sin∠BFC = BF / sin45˚
a / sin∠BFC = (√2)a / (1/√2)
1/2 = sin∠BFC
∠BFC = 30˚
∠BDE = ∠BFC = 30˚
length of the perpendicular from B to DE
= (√2)a x sin30˚
= (√2)a / 2
= a / √2
收錄日期: 2021-04-25 16:52:26
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070409000051KK00684