Question 1753
undecagon...means 1-10sided ie 11-sided. Learn Latin :-)

Interior angles...any shape can be split into triangles..a quadrilateral (any 4-sided figure) can be split into 2 triangles, so:

3-sided figure = 1 triangle, so interior angles add up to 180
4-sided figure = 2 triangle, so interior angles add up to 360
5-sided figure = 3 triangle, so interior angles add up to 540
6-sided figure = 4 triangle, so interior angles add up to 720
etc. No formula to learn, just understand that each shape can be made up of triangles... 40 sided figure is made up of 38 triangles therefore interior angles are 38x180 = 6840degrees.

Given an interior angle sum...divide it by 180. If you get a whole number then that is possible to have a polygon.

All in all, so many questions on polygons...learn the basics from your notes and try to answer them and then when you get really stuck and have looked in a textbook, come here and ask a specific question rather than just writing every question you got :-D

Enjoy maths - they are just puzzles with a definite answer.
Jon.