Recall that the trigonometry defines the relationship between sides and angles of a triangle. Trigonometry and its functions, sine, cosine and tangent, have an enormous number of uses in our daily life. For instance, it is used to measure height of a building or a mountain, in surveying, in aviation and also in the satellite navigation system. In this sub-topic, we will consider some practical examples on real life problems to understand the use of trigonometry.

The Law of Sines can be used to solve oblique triangles in which either two angles and a side or two sides and an angle opposite one of the sides are known.

The Law of Sine

If A, B, and C are the measures of the angles of a triangle ABC and a, b, and c are the lengths of the sides opposite these angles, then

The Law of Cosines can be used to solve triangles in which two sides and the included angle (SAS) are known or in which three sides (SSS) are known.