Question

If a regular octagon ABCDEFGH has sides that are 2 units long, what is the area of triangle ADG?

Answer 1

I know that <GHA is 135 degrees, which makes <AGH and <GAH both 22.5 degrees

Answer 2

Here's a slightly different approach. Maybe a bit quicker?

Essentially, drawing all the possible diagonals from a vertex cuts up the interior angle into equal smaller angles, so if the interior angle is 135°, then you know right away that <GAH=22.5°, and <GAD=67.5°.