三角形（さんかくけい、sankakukei）
- triangle

The Japanese word 三角形 (さんかくけい) means "triangle". It refers to a geometric shape with three sides and three angles. It's a fundamental concept in mathematics and is used to describe various objects and structures in the real world. A [三角形] is a polygon with three edges and three vertices.

⚫︎この絵には、たくさんの三角形があります。 Translation: There are many triangles in this picture. ⚫︎三角形の面積を計算してください。 Translation: Please calculate the area of the triangle. ⚫︎その家の屋根は三角形の形をしています。 Translation: The roof of that house is shaped like a triangle.

You use 三角形 when discussing anything related to triangles: their properties, the shape of objects, or calculations involving them. It’s used in math lessons, describing architecture, art, and everyday situations. It can be used both formally and informally.

The word is typically written with the kanji 三角形, but it can also be written in hiragana as さんかくけい. The kanji is the most common way to write it. The okurigana (送りがな) for 形 is "けい".

There aren't many direct synonyms for 三角形. It is a very specific term. However, you might use more general terms like "shape" (形 - katachi) or "figure" (図形 - zukei) when referring to it in a broader context.

There aren't direct antonyms for 三角形 in the sense of a single word. However, you could consider terms for other geometric shapes, such as "square" (四角形 - shikakkei), "circle" (円 - en), or "polygon" (多角形 - takakkei) as opposites in terms of shape.

数学の授業で、三角形の性質を学びました。 ・Translation: In math class, we learned about the properties of triangles. ・Explanation: This sentence explains that the speaker studied the characteristics of [三角形] in their math class.

この橋は三角形の構造で支えられています。 ・Translation: This bridge is supported by a triangular structure. ・Explanation: The sentence illustrates a practical application of the [三角形] shape, the bridge's support structure.

The word 三角形 is a combination of three kanji: 三 (san) meaning "three", 角 (kaku) meaning "corner" or "angle", and 形 (kei) meaning "shape" or "form". Thus, the literal meaning is "three-cornered shape", which accurately describes a triangle.