Question: prove that opposite angles of an isosceles trapezium are supplementary?
Answer: THEOREM: If a quadrilateral is an isosceles trapezoid, the opposite angles are supplementary. THEOREM: (converse) If a trapezoid has its opposite angles supplementary, it is an isosceles trapezoid. A kite is a quadrilateral whose four sides are drawn such that there are two distinct sets of adjacent, congruent sides.