I finally understand the difference between a closed, flat, or open universe. In a flat universe a triangle equalls 180 degrees I did not understand meaning of that statement. I just finnished reading a book by Leonard Susskind; "the father of string theory." Anyways a flat universe means that the expansion rate of the universe is constant, a closed universe means that the universe is shrinking and a open universe the expansion is accelerating. With a flat universe the triangle is not being distorted so sum of all the angles equal 180 degrees.