I'm reposting from here, but I'm not sure how to use the law of cosines on it, as I don't know any sides.
22.
The law of cosines can be used to determine a side of a triangle if two sides and the angle between them are known.
23.
Of any triangle, if you count the Law of Cosines, since it can be Black Carrot 05 : 31, 13 July 2007 ( UTC)
24.
For instance, propositions twelve and thirteen of book two of the " Elements " are the laws of cosines for obtuse and acute angles, respectively.
25.
In the 15th century, Jamsh + d al-Ksh + provided the first explicit statement of the law of cosines in a form suitable for triangulation.
26.
The law of cosines may be used to prove Heron's formula, which is another method that may be used to calculate the area of a triangle.
27.
For this you will need the diagonals, which can of course be found using the Law of cosines .-- talk ) 21 : 03, 24 May 2007 ( UTC)
28.
:If you know one of the angles ( preferably the one opposite the longest side ), you can use the law of cosines to calculate the length you need.
29.
The law of cosines for this tetrahedron, which relates the areas of the faces of the tetrahedron to the dihedral angles about a vertex, is given by the following relation:
30.
The law of cosines, or cosine rule, connects the length of an unknown side of a triangle to the length of the other sides and the angle opposite to the unknown side.
