dilloncyh 2010-7-21 03:47 PM
math problem
1. [draw]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[/draw]
If DE//BC, then AD/DB = AE/EC, but what reason should I write?
nofairnessatall 2010-7-21 03:54 PM
Equal ratios theorem,
but you can simply prove by similar triangles
021044 2010-7-21 04:10 PM
yes, equal ratio theorem~~~~~
kctsui75 2010-7-21 04:59 PM
equal ratios theorem 等比定理
or
intercept theorem 截線定理
均可！
dilloncyh 2010-7-22 08:05 AM
new question: when proofing two similiar triangles, if I wan to use the reason 'AAA", do I need to prove all three angles or two is already ok?
手槍仔仔 2010-7-22 08:19 AM
[quote]原帖由 [i]dilloncyh[/i] 於 2010-7-22 08:05 AM 發表 [url=http://lsforum.net/board/redirect.php?goto=findpost&pid=2256205&ptid=145080][img]http://lsforum.net/board/images/common/back.gif[/img][/url]
new question: when proofing two similiar triangles, if I wan to use the reason 'AAA", do I need to prove all three angles or two is already ok? [/quote]
two is acceptable =] but the reason still must be AAA (not only AA)
桃子 2010-7-27 01:03 PM
[quote]原帖由 [i]dilloncyh[/i] 於 2010-7-22 08:05 AM 發表 [url=http://lsforum.net/board/redirect.php?goto=findpost&pid=2256205&ptid=145080][img]http://lsforum.net/board/images/common/back.gif[/img][/url]
new question: when proofing two similiar triangles, if I wan to use the reason 'AAA", do I need to prove all three angles or two is already ok? [/quote]
In recent years' marking schemes, you can omit the third angle.
However, marking scheme may vary from year to year. It is always safer to prove all three angles.
My teacher claimed there was a year that 1 mark was deducted for not proving the third angle.
lmw 2010-8-5 09:11 AM
Intercept Thm . . you can find it in the F.3 textbook.
it is in the topic with mid-point Thm as well . . .. .