Introduction to Trigonometry

Many mathematicians knew about similar triangles and angle measurements. However, they had faced a problem, as stated below:

If I know the 3 sides of a triangle, am I able to find all 3 angles?

In the past, the only thing people could do was to construct the triangle with a compass and measurements. They initially defined 3 quantities related to the angle measured in a right angle triangle, known as the sine, cosine and tangent:



As in the diagram above, we define sin(A)=a/h, cos(A)=b/h and tan(A)=a/b. Later, they came up with a table of values that would be convenient for reference later on. An image of it is displayed below:



We will discuss some of their properties in later tutorials.