1, a set of quadrangles with parallel opposite sides and another set of quadrangles with non-parallel opposite sides are trapezoid.

2. A set of quadrilaterals with parallel and unequal opposite sides is a trapezoid.

Trapezoidal characteristic

1, the top and bottom of the trapezoid are parallel;

2. Trapezoidal midline, parallel to the two bottoms, equal to half of the sum of the upper and lower bottoms;

3. The diagonal lines of the isosceles trapezoid are equal.

Extended data isosceles trapezoid

1, the two waists of an isosceles trapezoid are equal.

2. The two bottom angles of the isosceles trapezoid on the same base are equal.

3. The two diagonals of the isosceles trapezoid are equal.

4. The isosceles trapezoid is an axisymmetric figure, and the symmetry axis is a straight line connecting the midpoints of the upper and lower bottom surfaces.

5. The midline of the isosceles trapezoid (the same is true for this non-isosceles trapezoid) (the line connecting the two waist midpoints is called the midline) is equal to half of the sum of the upper and lower bottoms.

6. A trapezoid with an angle of 90 is a right-angled trapezoid.