Grade 3Math
Isosceles and Equilateral TrianglesPay attention to the length of the sides
When you compare the lengths of the sides of triangles, there are triangles with two sides of equal length, and triangles with all three sides of equal length.
The narration and the pictures are in Japanese. You can hear the same words that are used in class at a Japanese school.
- Video
- 2:29（8 scenes）
- Problems
- 2 problems
Open this lesson in Japanese（二等辺三角形と 正三角形）
Let's try
Write the math sentence in your notebook first, then open the answer.
-
1Looking at the fact that all three sides are the same length, what is the name of the triangle?
Hint
Think about how many sides are equal.
Answer
It is an "equilateral triangle."
-
2What do you call a triangle where only two sides are equal and the other side has a different length?
Hint
In Japanese, the name of this triangle starts with the word for "two."
Answer
It is an "isosceles triangle."
Words in this lesson
- isosceles triangle 二等辺三角形
- A triangle with two sides of equal length.
- equilateral triangle 正三角形
- A triangle with all three sides of equal length. It is also a kind of isosceles triangle.
- compass コンパス
- A tool for drawing circles and copying lengths.
For parents and guardians
- The names of lessons and the order of topics differ slightly between textbooks. This page follows the content of Japan's national curriculum guidelines (the Course of Study).
- A compass is used not only for drawing circles but also as a tool for copying and comparing lengths. Drawing isosceles and equilateral triangles with a compass at home, following the same steps as on the screen, deepens understanding.
- This page mentions that because an equilateral triangle has three equal sides, it is also a member of the isosceles triangles, which have two equal sides. The compass lines in the drawing scenes are shown on the screen as arcs.