For this task you need the following basic knowledge: Sine, Cosine and Tangent
If you now draw a line from the intersection of the diagonals to the centre of the side , then the angle you are looking for is divided into two equal parts by this auxiliary line.
There are several ways to calculate the angle :
The solution with the tangent is mathematically easier .
Solution with the sine
First we calculate the distance from to and thus obtain a right-angled triangle.
To calculate the angle , we divide the distance from to and the distance from to by . Thus we can apply the sine to calculate . Then we multiply the calculated angle by and get the angle we are looking for, .
Solution with the tangent
Consider the triangle . This triangle is right-angled.