Best Answer

We use the law of Cosines to be able to find :

1. The measure of the third side, when the measure of two sides and the included angle of a triangle ABC are known.

2. The measure of any angle, when the measure of the three sides of a triangle ABC are known.

Q: When do you use the Law of Cosines?

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Trigonometric ratios, by themselves, can only be used for right angled triangles. The law of cosines or the sine law can be used for any triangle.

A caveman from 10,000 BCal-Kashi was the 1st to provide an explicit statement of the law of cosines in a form suitable for triangulation

Use the law of cosines (look them up on wikipedia).

Yes, absolutely

When none of the angles are known, and using Pythagoras, the triangle is known not to be right angled.

Law of cosines

Having sufficient angles or sides one can use either, The Law of Sines, or, The Law of Cosines. Google them.

true

The law of cosines with a right angle is just the pythagorean theorem. The cosine of 90 degrees is 0. That is why the hypotenuse squared is equal to the sum of both of the legs squared

The law of cosines can be written in one form as: c2 = a2 + b2 - 2abCos C. Without 3 of the 4 variables being given, there is no way to answer this question.

cosine = adjacent/hypotenuse

Yes