If you are looking for a website to manipulate polygons, try Visnos's Polygon Explorer. When you open the site you will see the image below.
A few things to point out
- in the upper right you will see
- a protractor that you can measure each angle
- next to the protractor you will see a ruler that you can measure sides
- next to the ruler is drag which is the ability to toggle off the circles around each vertex
- this is important especially when using the protractor as you will then not move the vertex by mistake
- finally you will see 0.5 - you can adjust this as it allows you to drag the vertex
- at 0.5 you can position each vertex by 0.5
- from 3 to 20
- from 0 to 10
- from 0 to 360
- under the angle you will see
- outer and then interior
- when you select them you will then see the angles
Embedded below is a 2 minute long YouTube tutorial.