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標題: F.3數3題 [打印本頁]

作者: billyconan 時間: 09-12-21 02:20 PM 標題: F.3數3題

我唔識做ar

圖片附件: 未命名.JPG (09-12-21 02:20 PM, 57.78 KB) / 下載次數 20
https://www.2000fun.com/forum.php?mod=attachment&aid=MjQ5NTM1fDIzYTUyZWYxfDE3NTQzNTYzMjJ8MA%3D%3D

作者: 富商.豪 時間: 09-12-30 09:03 PM

5.  OB^2 = 12^2 + 9^2
   OB = 15unit

(OB x PA)/2 = (OA x 9)/2  <-- area=area
   15PA    = 6 x 9
            PA = 54/15 = 18/5 unit

6. A,B,C are collinear
so,slope of AB = slope of AC
         (2a-a) / (1+2) =  (a+1)/(-2-7)
                     3a + 3 = -9a
                                 a = -1/4

7.  let <ABE = <EBC = a , <ACD=<DCB=b.
   AB=AC(given)
so, <ABC = < ACB (base angle,isos. tri.)
         <DCB = < EBC    <---  2a=2b
            BC = BC ( common side)
so,tri. BCE and  tri. CBD  are congruent.(A.S.A)
so,  <BDC=<CEB = 90 degree (corr. angle of cong. tri.)
   therefore,CD is an altitude of tri. ABC

應該冇計錯掛...

[ 本帖最後由富商.豪於 09-12-31 06:40 PM 編輯 ]

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