**Answer:**

1.There are five ways to prove that a quadrilateral is a parallelogram:

Prove that both pairs of opposite sides are congruent.

Prove that both pairs of opposite sides are parallel.

Prove that one pair of opposite sides is both congruent and parallel.

Prove that the diagonals of the quadrilateral bisect each other.

2.In Euclidean geometry, an isosceles trapezoid (isosceles trapezium in British English) is a convex quadrilateral with a line of symmetry bisecting one pair of opposite sides. … Alternatively, it can be defined as a trapezoid in which both legs and both base angles are of the same measure.

3.???

**Step-by-step explanation:**

Pasensya na po talaga sa 3. du ko po talaga alam sorry sorry po talaga