Question

prove that the opposite angles of an isosceles trapezium is supplementary

Answer 1

DEFINITION: An isosceles trapezoid is a trapezoid with congruent base angles.
THEOREM: If a quadrilateral (with one set of parallel sides) is an isosceles trapezoid, its legs are congruent. ...
THEOREM: If a quadrilateral is an isosceles trapezoid, the opposite angles are supplementary.