I have a pentagon that I have split into 5 triangles and was wanting to say that the sum of the triangle's angels is 900 and the sum of the 5 middle angles formed by the points of the triangles is 360, therefore the pentagon's angle sum is 900-360 = 540. How can I express this all in mathematical notation?

If I labelled the triangles from 1-5 and the angles from a-e in my diagram, could I say:

or something?