What is the basic difference between the Law of Sines and Law of Cosines?
The cosine rule relates the cosine of an angle of a triangle to the sides of the triangle. With its help , the angles of a triangle can be determined , if all its sides are known.
The sine rules gives the ratio of the sine of two angles of a triangle, which equals to the ratio of the corresponding opposite sides. With its help we can determine any one of these four elements, if other three are known.