Naive means unsuspecting. An example might be, "It was very naive of Tommy to think that the former criminal would help him"
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.