The strongest shape.
A polygon with three edges and three vertices. Internal angles always sum to 180°.
The strongest structure in architecture because it cannot change shape without breaking a side.
All angles inside MUST add up to 180 degrees.
In Plain English: Triangles are the bedrock of shapes. Unlike a square, which can tilt into a diamond, a triangle is rigid. That is why bridges are made of them.
In The Real World: Construction. Roof trusses are triangles to prevent the roof from collapsing.
Assuming a triangle is a Right Triangle just because it looks like one. Never assume 90 degrees unless you see the little square box.