Triangle
noun, の adjective
You already learned that 三角 means "triangle." Well this means triangle too, but it's the mathematical term. You should use it in math class.
さんかくけい, さんかっけい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
これが、三角形のおにぎりの作り方です。
This is how to make a triangular rice ball.
このキッチン、三角形のタイルが、かわいいですね。
Triangular tiles in the kitchen are cute.
この三角形のグラフで、何が分かるんですか？
What can you tell from this triangular graph?