Properties of triangles are
1. the three vertices
2. the base which is present in every triangle
3. altitudes of the triangle
4. median of the triangle
5. area of the triangle
6. perimeter of the triangle
7. interior and exterior angles of the triangle

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Properties of a triangle are

0.  Any triangle  is in a single plane.

1   the relationships between the sizes of the sides.
           a + b > C > | a - b |

2   the relation ships between the interior angles 
            Sum of A, B, C is 180 degrees.

3   the relationships between the angles and the sides

4.  the relationship between interior and exterior angles.

5.  relationship between area, perimeter, center of gravity, circumcircle, incircle etc. and the sides.