Write 25 properties of a triangle

Here is your answer to your query:

They are three sided polygons.
The sum of all interior angles is 180 degrees.
The sum of any two sides of a triangle is greater than the third side.
The difference of any two sides is less than the third side.
The sides opposite to equal angles are always equal and vice versa. 
An exterior angle of a triangle is equal to the sum of interior opposite angles.
The sum of exterior and the adjacent interior angle is 180 degrees. 
The median divides the triangle into two triangles of equal area. 
Two triangles of the same base between same parallel lines are of equal area. 

Hope this cleared your doubt. 
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