I am autistic and have difficulty understanding certain things for (sometimes) no apparent reason. This is one of those times. I am in need of help, and would appreciate some explanation. Thankyou! Please simplify it as much as possible.
In: 7
I assume you know how sine & cosine are used (at least in terms of SOHCAHTOA) and just need help understanding these 2 rules. If you want to know what sine & cosine actually are, that’s another topic.
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**Cosine rule**
You know the Pythagorean Theorem, correct? Well, that only works for a right (90°) triangle. If it isn’t a right triangle, that’s where the cosine rule can come into play. [**Here is the proof**](https://mathspace-production-media.mathspace.co/media/imagecontent/cosine_law_proof.gif). You basically split it into 2 triangles, both now right-angled, so you use Pythagorean Theorem on both, combine them, and you get the cosine rule.
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**Sine rule**
The sine rule is just basic algebraic manipulation. [**Here is the proof**](https://www.geogebra.org/resource/ADJFzYAr/nvqaSonSqFBFKzo6/material-ADJFzYAr.png). It involves converting a triangle into 2 right angled ones like for the cosine rule, then use the SOHCAHTOA to define an angle on each triangle, isolating the 90° side, then setting the equations equal to each other.
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