f3 mth questions!!!急~

2011-03-01 4:30 am

6. In the figure, ABCD and BFEC are parallelograms. Prove that
(a) AD//FE,

(b) AD = FE,

(c) AFED is a parallelogram.

12. In the figure ,ABCD is a parallelogram.Both AE and CF are perpendicular to the diagonal BD,and BE = FD.

(a) Prove that AE = CF

(b)Join AF and EC.Prove that AECF is a parallelogram.

求step,thx~~
一定要有完整啲step~~(一定要有(< sum of △)lee d公式!!)唔好亂做,一定要岩同埋要清楚(要睇得明你寫咩)!!!!thx~~

去LEE到就有圖:
http://www.uwants.com/viewthread.php?tid=11603862&extra=page%3D1

回答 (1)

魔龍帝齊格益力多

2011-03-01 4:42 am

✔ 最佳答案

BC//FE(prop. of //gram)
AD//BC(prop. of //gram)
AD//FE
________________
AD=BC(prop. of //gram)
BC=FE(prop. of //gram)
AD=FE
_________________
AD//FE(proved),AD=FE(proved)
AFED is a parallelogram.(2 sides equal and //)
___________________________________________
ABD=BDC(alt. angles,AB//CD)
BE=FD(Given)
AEB=DFC=90
ABE=CDF(ASA)
AE = CF(corr. sides,~=tri.)__________Join AF and EC.Prove that AECF is a parallelogram.AEF=180-90(adj. angles on a st. line)=90
CFE=180-90(adj. angles on a st. line)=90
AE//FC(alt. angles, equal)
AE=FC(proved)
AECF is a parallelogram.(two sides equal and//)

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