長径

1. Origins, structure, and basic meaning

• Structure: 長径 is read as ちょうけい and is a noun for the major axis of an ellipse or the length across its longest central direction.
• Basic usage: Measurement appears in 楕円の長径を測る, while the paired axes appear in 長径と短径.

2. Common pitfalls and similar expressions

• Contrast with 短径
  • 長径 is the ellipse’s longer direction; 短径 is the shorter perpendicular direction.
• Line and length
  • Context can refer to the axis itself or its measured length, so the diagram and numerical wording matter.