HG 11
D14. A degree is one one-ninetieth of a right angle.
T15. The sum of two angles of a triangle is less than 180° .
T16. Given triangle ABC and angle A. Then there exists a triangle A1B1C1 such
that triangle A1B1C1 has the same angle sum as triangle ABC, and angle Al
is less than or equal to one-half angle A.