mặt nón

Definition

1. Noun (Geometry):
   • Cone (surface): In geometry, a "mặt nón" is the curved surface of a cone. It is specifically the lateral surface generated by rotating a right triangle around one of its legs (perpendicular sides). The term refers to the two-dimensional surface, not the solid three-dimensional figure.

Usage Examples

• Noun:
  • Diện tích của mặt nón được tính bằng công thức πrl. (The area of the cone's lateral surface is calculated by the formula πrl.)
  • Trong hình học, chúng ta phân biệt giữa mặt nón và hình nón. (In geometry, we distinguish between the conical surface and the solid cone.)

Advanced Usage

• "mặt nón cụt": Truncated cone (surface) / Frustum (lateral surface).
  • Công thức tính diện tích mặt nón cụt phức tạp hơn. (The formula for calculating the area of a truncated conical surface is more complex.)

Variants and Related Words

• Hình nón (n): Cone (the solid figure).
  • Thể tích của hình nón là (1/3)πr²h. (The volume of a cone is (1/3)πr²h.)
• Đường sinh (n): Generatrix (the line segment that generates the surface).
  • Độ dài đường sinh của mặt nón thường được ký hiệu là l. (The length of the generatrix of a conical surface is usually denoted by l.)

Synonyms

• Conical surface
• Lateral surface of a cone

Notes on Usage

• "Mặt nón" is a specialized mathematical term. In everyday language, the word "nón" alone typically refers to a conical hat (like the Vietnamese leaf hat). The geometric meaning is only clear in a scientific or mathematical context.
• It is crucial to distinguish it from "hình nón", which refers to the solid cone including its base. "Mặt nón" refers only to the slanted, curved surface.