Law of cosines |

Three angle of the triangle gives three options for the formula of one triangle. In law of cosines can use a one formula, and three variants of symbols.

Three variants of symbols |

These two options allow to describe all sides and angles of the triangle. The traditional problems of mathematics we are taught to find one of the triangle elements.

**Question: Can one formula with one variant of symbols to describe all the elements of the triangle?**

Answer: Yes, you can.Here's how to do it using the cosine theorem.

Answer: Yes, you can.

The proof of the theorem of cosines in the trigonometric form looks like.

The proof using trigonometry |

If you change the "minus" sign in the "plus" sign, we get the cosine theorem for the perimeter of the triangle.

Law of cosines in general form (in Russian).

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