可計算兩平面之交角的神秘公式，HKDSE 考生絕不能錯過！

[@chunyulo7605]

直接用坐標，把B設為(0,0), C(31.93,0), A(x,y) AB 長 60， BC長 31.93，AC 長 40 , 用坐標長度可計算出A 的x , 然後就求到角ABC 大小。 所有三角形只要有3邊，放入坐標是一定可以求出所有角。

[@chandanny9521]

正，最緊要考評局都接受！

[@garysuen3796]

HKEAA似走火入魔多的直接鼓勵用out of syllabus既方法 。識用都唔簡單

[@向世界出發大J看世界]

話哂大學入學試 所以出好多out syllabus 既野

[@jonathanchan9519]

Gary Suen out syllabus 未必會有分 同埋就係正正係level 4 嘅同學先會直接放平時補習學嘅formula Level 5** 嗰d一定可以用到in syllabus 嘅野計到 淨係用out syl 黎check 數

[@wahanwang6068]

不過很奇怪，正常來說不在範圍內的數學知識不能用作答卷，正如不能使用微積分來作管卷一的題目，但為何又可以用二面角公式呢？

[@jasonchan4662]

真係好有個用,救到命

[@나강원-c6d]

感謝分享! 在下有個小疑問望得解答：如考題要求學生計算二面角的餘弦值，並用根式表示答案，這條公式是否無效？

[@peter021044]

睇吓題目有幾樣衰 你過程中因為已經用了out c 如果牽扯到m2用到compound angle已可以照用 都out c啦😂

[@你不聽搖滾]

Thank you!

[@harrisonshek7472]

2:16

[@zinglahmyearn2576]

can only apply this formula when it is a tetrahedron?

[@mathseasy]

喺 1:24 已經講得好清楚。

[@salts9642]

我老師唔接受呢個方法😂

[@peter021044]

唔明邊隻打邊隻可由4：36開始睇

[@tamsir3175]

btw thank you very much for your contribution and effort

[@tamsir3175]

我成日睇你的channel.學到嘢😊

[@namelness8319]

多謝

[@mryip06]

用2次cos law就可以證明，我稍後整下

[@ArChungLing]

考試用有冇步驟分?

[@mathseasy]

Watch my explanation here: kzbin.info/www/bejne/ZoC3hZKBe5aVidU&t=944

[@guythat29]

@@mathseasy 但係Marking scheme特別指明你用咗呢條公式0M0A

[@mathseasy]

@@guythat29 你是在那裡找到這註釋？ 在公開的 marking scheme 和 report 都無這樣說。

[@guythat29]

@@mathseasy dse00.blogspot.com/p/mathdse.html?m=1

[@mathseasy]

@@guythat29 這份 Marking Scheme 應該是假的。 有自稱是老師和已買卷的人都說可取全部分數。 Anyway, Thank you for your information! lihkg.com/thread/939293/page/1

[@galaxy-ff5yw]

超正！！！thanks a lot

[@tiklee7446]

你計pp 18 b計到？

[@galaxy-ff5yw]

@@tiklee7446？同呢條式唔關事

[@winnieleexh]

Tetrahedron 計兩個面之間嘅角嘅時候，其中有兩隻角相鄰，係米兩面都計到？ 以你個模型黎講 你用紅綠藍去計紅藍之間嘅角，但用紅藍白係米都有異曲同工之妙？ sorry for1999

[@mathseasy]

Yes, 用另一面的頂點都計到。

[@tiklee7446]

計 pp18b 點解唔得！

[@pchungpchun6656]

This video tries to summarize how an angle between two given planes, one popular subject examined in HKDSE, might be dealt handily with the dihedral angle "formula". The video does not mention its proof of any. The video's educational intent could likely rest on "motivating" mathematics learning of those who could still find intuitive workings tedious for relevant problems to consider one possible short-cut against a potentially "more favourable" outcome, especially when associated problem-solving contexts could make them "illusive" from time to time. This does not mean that followers can escape from risking their outcomes before their full understanding. If the subject is examined explicitly, then the major workings lie only and always on how to determine 2 connected altitudes of each on individual planes at a point on their common line of intersection. If a learner can however fail to manage this concept or the associated attitude for underlying workings, how could s/he manage understanding the proof of the dihedral angle "formula" or solve such a level of problems confidently? This video's suggested "method" of learning looks contradictory to why the subject should be learnt, although I still appreciate the teacher's effort in making up this video.

[@ok-js3tp]

skill issues

[@knenaa_]

Work smarter not harder.

[@iwjrbf99]

L

[@ethangamingproduction7473]

請問2020年考生學咗呢條公式有冇着數？

[@mathseasy]

有着數就學，無着數就唔學??

[@ethangamingproduction7473]

我嘅意思係想問下出用得着呢個技巧嘅題目機會高低🙏🏻

[@ethangamingproduction7473]

抱歉令你誤會我意思

[@biliibalaaa5747]

sir 我仲係唔識分辨 紅色同藍色果隻角🙏

[@biliibalaaa5747]

不太明白🥵🙏

[@tszkit5254]

啊sir，即係hkeaa接受用呢條公式去計答案而攞到full marks？ 我係18Dse數5*，今年想重考多次。所以想問清楚thx

[@mathseasy]

已我所知是可以取全部分數。從來考評局都接受課程以外的方法。 利申：沒有參與評卷工作。如果有評卷老師或已買卷的同學知道一手資料的話，希望可留言提供資料。

[@tszkit5254]

@@mathseasy 咁如果用M2方法做core也接受嗎？

[@mathseasy]

@@tszkit5254 無問題。但可用到 M2 方法的機會實在唔多。

[@Tom-ih7hj]

學校沒有教的數學 不可取全部分數 前面仲有一堆野可以"背" 去prove 條式出黎， 背左就full ,直出條式就扣1~2分

[@mathseasy]

@@CJ777-e2g Out Syl 的方法是否可用這問題，我已經無力氣再去解釋了。

[@pipperlong]

Like!!!!

[@jimmyli319]

Holy sht it works!

[@tamsir3175]

唔用這公式都好易計到。两個平面之間的夾角是很基礎的題目。

[@brian_kam]

癲