First of all, a brief introduction.

A trapezoid is a quadrilateral with only a set of parallel opposite sides. Parallel sides are called trapezoidal bottoms: the longer bottoms are called bottoms, and the shorter bottoms are called bottoms; The other two sides are called waist; The vertical section sandwiched between the two base sides is called the height of the trapezoid. A trapezoid whose waist is perpendicular to the bottom is called a right-angled trapezoid.

Second, related knowledge

1. Judgment: A set of quadrangles with parallel opposite sides and another set of quadrangles with non-parallel opposite sides are trapezoid; A set of quadrilaterals with parallel and unequal opposite sides is a trapezoid; Definition of isosceles trapezoid: two trapezoid with equal waist are called isosceles trapezoid; Nature: the two waists of an isosceles trapezoid are equal; The two bottom angles of the isosceles trapezoid on the same base are equal; The two diagonals of an isosceles trapezoid are equal.

2. The waist trapezoid is an axisymmetric figure, and the symmetry axis is a straight line at the connecting line between the middle points of the upper and lower bottoms (a straight line passing through the middle points of the two bottoms); Judgment: isosceles trapezoid is isosceles trapezoid; Two trapezoid with equal angles on the same base are isosceles trapezoid; A trapezoid with equal diagonal lines is an isosceles trapezoid.

3. Definition of right-angled trapezoid: A trapezoid whose waist is perpendicular to the bottom is called a right-angled trapezoid; Properties: right-angled trapezoid, in which two angles are right angles; It has certain stability, but it is weaker than non-right trapezoid; Judgment: the trapezoid with the waist perpendicular to the bottom is a right-angled trapezoid; A trapezoid with a right angle inside is a right-angled trapezoid.

Third, the area

1. When the space occupied by an object is a two-dimensional space, the size of the space occupied is called the area of the object, which can be plane or curved. Such as square meters, square decimeters, square centimeters, etc. Is a recognized unit of area, which can be expressed as (m? ，dm？ ，cm？ )。

2. Area is a number indicating the degree of two-dimensional figure or shape or plane layer in a plane. A surface region is a simulation on a two-dimensional surface of a three-dimensional object. Area can be understood as the amount of material with a given thickness, which is necessary to form a shape model.