WHY must a heptagon add up to 900° (in pictures)
Because there are now 5 triangles in a heptagon and it must add up to `5times180°=900°`.
The heptagon can be made from 5 triangles.
An equilateral heptagon will have 7 equal internal angles and would be
Each internal angle is 128.57°.
But the interior angles would still add up to 900°.