- If two sides of a triangle are unequal, the greater side has the greater angle opposite to it.
- If two angles of a triangle are unequal, the greater angle has the greater side opposite to it.
- The sum of any two sides of a triangle is greater than the third side.
- In a triangle, the difference in the lengths of any two sides is less than the third side.
- Of all the straight lines that can be drawn to a straight line from a given point outside it, the perpendicular is the shortest.