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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.
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Language Fluency
| Tagalog | Native |
|---|---|
| Englisch | Near-Native |
| Japanisch | Just a few words |
| Koreanisch | Just a few words |
| Spanisch | Just a few words |
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