Together with the law of sines, the law of cosines can help in solving from simple to complex trigonometric problems by using the formulas provided below. These calculations can be either made by hand or by using this law of cosines calculator. Using the distance formula, In the preceding formula, if γ is 90°, then the cos 90° = 0, yielding the Pythagorean theorem for right triangles. If the orientation of the triangle is changed to have A or B at the origin, then the other two versions of the Law of Cosines can be obtained. Two specific cases are of particular importance. See also Law of Sines. The Law of Cosines is a tool for solving triangles. That is, given some information about the triangle we can find more. In this case the tool is useful when you know two sides and their included angle. From that, you can use the Law of Cosines to find the third side. It works on any triangle, not just right triangles. Anyway, the law of cosines involves a triangle like this, where our sides are labeled a, b and c. And then we have one angle, like A here. The law states that a 2 = b 2 + c 2 - 2 bc (cos A ). II. Determine whether the Law of Cosines or the Law of Sines is the best choice. 1. State whether the Law of Sines or Law of Cosines is the best choice to solve for x for the given figure. Substitute the values in to the appropriate formula (do not solve). 2. State whether the Law of Sines or Law of Cosines is the best choice to solve for x for Learn law of cosines math with free interactive flashcards. Choose from 500 different sets of law of cosines math flashcards on Quizlet. ... Law of Cosines Formula.