Law of cosine is also known as cosine rule. The law of cosines is the law that is applicable when calculating one side of a triangle when an opposite angle and other two sides are well known. In general law of cosine is useful when finding the third side of a triangle when two sides are well known and when finding the angle of a triangle when all sides of a triangle are known.  For any triangle, a, b and c are the sides while C is the angle that is opposite to side c.  Law of cosine is useful when solving mathematical problems of triangles. The law of cosine is written as c2=a2+b2-2ab cos (C). for the right-angled triangles, the formula used is a2+b2=c2. The law of cosine can be used together with the law of sines when finding all angles and sides.   The law of cosines is applicable in vector quantities.  The law of cosines and law of sines are used the plane heading and proceeding to the desired bearing to a destination. The law of cosine in an obtuse triangle is known to the negation of cosine of the supplement. The cosine rule is represented as a geometric result in relation to parts of a triangle.

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