What's the tool used to create geometry illustration graphics on wikipedia
When I read articles about geometry/graphics on wikipedia, I see some very clean illustration graphics, for example:

![enter image description here][1]
![enter image description here][2]
![enter image description here][3]


  [1]: http://i.stack.imgur.com/nDJFU.png
  [2]: http://i.stack.imgur.com/yu1Q2.png
  [3]: http://i.stack.imgur.com/wiaNM.png

Is there any way to create graphics like this easily?
What's the tool used to create geometry illustration graphics on wikipedia
===

When I read articles about geometry/graphics on wikipedia, I see some very clean illustration graphics, for example:

![enter image description here][1]
![enter image description here][2]
![enter image description here][3]


  [1]: http://i.stack.imgur.com/nDJFU.png
  [2]: http://i.stack.imgur.com/yu1Q2.png
  [3]: http://i.stack.imgur.com/wiaNM.png

Is there any way to create graphics like this easily?