日本語
한국어
简体中文
繁體中文
Italiano
español
Deutsch
Русский
Proof of Cosine Law
Natz
Sep 7, 2025
I want to walk you through a proof of the cosine law—but with a twist. We’re looking at a case where one of the angles is obtuse. This often feels tricky at first, but with the right tools and a bit of reflection, it becomes beautifully clear.I love this proof because it shows how math builds on itself. Even when things get less intuitive—like with obtuse angles—we can lean on what we already know. If you’ve ever felt unsure about the cosine law in non-right triangles, I hope this helped make it feel more approachable.
This column was published by the author in their personal capacity.
The opinions expressed in this column are the author's own and do not reflect the view of Cafetalk.
The opinions expressed in this column are the author's own and do not reflect the view of Cafetalk.
Lesson
from:
in:
Lesson Categories
Language Fluency
| Tagalog | Native |
|---|---|
| English | Near-Native |
| Japanese | Just a few words |
| Korean | Just a few words |
| Spanish | Just a few words |
Natz's Most Popular Columns
-
Coping With Stress Before Exams
Stress has always been part of the lives of not only adults but more so of students. There's ...
Natz
06931Jul 1, 2019 -
Hello dear students! I have opened additional slots for my classes here in Cafetalk. What I li...
Natz
06743Jul 18, 2019 -
I Don’t Have Gills But I Can Swim
Do you know which is as important as power kicks and arm pulls in swimm...
Natz
06708Jul 6, 2019 -
Autumn/Winter 2020 Academic Tutoring Category Award
Dear students and parents,You have been a big part of my achievements and my career as a whole on C...
Natz
04687Dec 18, 2020
People who read this post also read ...
-
こんにちは！いつも楽しく、積極的に、日本語を勉強してくださり、ありがとうございます！今日から、ゆるゆると、面白いなと思った動画をみなさんに共有していこうと思います。日本は、47都道府県（とどうふけん...
Hiroco.N
04734Jul 30, 2023 -
レッスンの生徒様、興味を持ってくださっている方、いつもありがとうございます！今さらながらですが、簡単な自己紹介を書きます。私はプライベートでは、インドアな方かもしれません。読書やライティングが好きで...
Eri.JAPAN
0641Aug 20, 2025 -
Longer classes for more effective learning!
Since the demise of Skype, more students and tutors are preferring to use Zoom. I certainly find it...
Liz English
4420Sep 4, 2025 -
こんにちは今回、カフェトーク講師サポートチームから嬉しいお知らせが届きました。カフェトークでのレッスンが10レッスン達成したそうです！！生徒の皆様、ありがとうございます。記念にコラムを書かせていただ...
nori.
0385Sep 1, 2025
Comments (0)