Ummm... A trapezoid is a quadrilateral and the quadrilateral sum theorem states that the sum of all angles in any given polygon can be found by solving (n-2)180 with n being the number of sides, so a trapezoid has 360 degrees. A DUH. I'm 15 and I know that...

Trapezoids have many helpful properties in Geometry. The rules that count for all trapezoids (and not only isosceles trapezoids): Trapezoids have two parallel sides, and two non-parallel sides. The angles of a trapezoid sum up to 180 degrees. The lower-base angles are each supplementary to their respective upper-base angles.