In search of the Polygon's Interior angles

On the fifth lesson, I was given a piece of square-shape paper.

Dr.Yeap: "Class, please turn this square-shape paper into a five-sided Polygon; you can cut, fold, or tear or  anything to turn it into a five-sided Polygon".

I questioned myself, what is Polygon? The last time this word came to me was few years back on my E-math 'O' Level paper". Well, does not matter, since I understand what does 'five-sided' means. Then, I folded oe side of the paper into a triangle. It looks like this:

                                                                Fig.1.Five-sided Polygon

Dr.Yeap:"Please find all the sum of the interior angles"

I am rather confident that the sum of those three pependicular angles at the corner are equivalent of 270 degree. But, how do I find the other two angles which are at the bottom? I was not so sure, but somehow I perceived that there has to be relation with the properties of angles in triangles in order to find this interior angles. 

Through observation, my thinking was reaffirmed that this polygon is a combination of a right-angle triangle and a trapezium. 

Here is my solution:

                                           Fig.2. Solution of Finding the sum of Interior Angles

After doing this exercise, I read the chapter on Geometry and my understanding got deepened; the concepts of right, obtuse, and accute angles, congruence of line segments and angles, and symmetry is a good way to help us to see how different collections of properties apply to special classes of shapes.

Then I went on to do my searching on the term Polygon; is a closed plane figure with three or more, usually straight, sides. Ehm,..three-sided? Does it mean triangle is considered as a Polygon as well? Yes, it does. 

Triangle is considered as a Polygon! A ha, now I remembered it! It was once said by my Math teacher back in Secondary School.