As stated in Lesson 1 Rough Perspective exercise, both ways are fine. It simply depends on what you want to check. Edges test your execution, while corners test your intent. You can try both ways on different pages and choose the one you like more.

One thing to note is that you should stick to one extension method on a page.

All of this is taken from Lesson 1 Rough Perspective exercise, Edges or Corners section. Give it one more read!