The interior angles in a triangle always add up to 180º. An equilateral triangle has 3 sides of equal length. The dashes on the lines show they are equal in length. All of the angles are also equal.

They often identify them solely based on their resemblance to prototypes: e.g., a shape will be called a triangle if it looks like an equilateral triangle with a horizontal base – all others are ...

Henry Dudeney, a self-taught English mathematician and puzzle columnist, asked his readers to dissect an equilateral triangle into the smallest number of pieces that could be rearranged into a square.

For example a pentagon is always a shape that has 5 sides. An equilateral triangle has 3 sides of equal length. The dashes on the lines show they are equal in length. All of the angles are also equal.

The ancient Greek mathematician Euclid proved in his Elements of Geometry that there are only five Platonic solids – the regular tetrahedron (four sides that are equilateral triangles), the cube (six ...

Big Idea – We can describe, measure, and compare spatial relationships. to build on students' knowledge of triangle and to develop students' reasoning with properties of triangle to develop students' ...