# Equilateral Triangle Facts for K6 Math

The Equilateral Triangle, is the fourth of six methods to identify triangles  in my Master Basic Geometry journey.

This shape is excellent to explain basic geometry with.  It is also fun later on, when the basics have been learned.

It can be used in the early stages of explaining tessellations before moving on to the more complex tessellations involving polygons with more than three sides! Your child must become familiar with the method of labeling polygons with line and angle symbols.

Take note of how this triangle is labeled.  All three sides, a, b and c have one dash through them, indicating they are the same length.

All angles are indicated with the same symbol, showing they are all equal in measure. In fact, they are always 60 degrees!

This is a standard method of indicating lines and angles in all polygons.

The area of an Equilateral Triangle is calculated in the same manner as ANY triangle.  It is always  ½ the base multiplied by the perpendicular height.

## Summary of the Facts

• An equilateral triangle:
• Has ALL THREE sides the same length and
• HAS ALL THREE angles equal in measurement.
• It CAN NOT be a Right Triangle
• It CAN NOT be an ﻿Obtuse Triangle﻿
• It is ALWAYS an Acute Triangle giving us an Acute-Equilateral Triangle.

Now is also a good time to introduce your child to the term equiangular. Equilateral makes reference to equal lines, while equiangular makes reference to equal angles.

So, if they are told a triangle is equiangular then they are being told that the triangle is equilateral!  Why?

For a triangle to be equiangular, it MUST have three angles 60 degrees in measurement.  This also tells us, that any equilateral-triangle, no matter its size always has three angles with a measurement of 60 degrees.

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