底辺

1. Origins, structure, and basic meaning

• Structure: 底辺（ていへん） means the side taken as the base of a shape.
• Basic usage: Use it when measuring a triangle or calculating its area.

2. Common pitfalls and similar expressions

• Base and height
  • In a triangle, 底辺 is the side chosen as the base; 高さ is the perpendicular distance from that side or its extension to the opposite vertex.