That depends on what textbook you use. The old version of the textbook of People's Education Press (revised in 2002) has been expanded in the parallelogram chapter (the second volume of the eighth grade), and the new version of the textbook of People's Education Press (revised in 20 13) has cancelled this part. In fact, as early as the People's Education Edition, the first volume of the fourth grade primary school mathematics has already had a trapezoidal understanding course. 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. An isosceles trapezoid is called an isosceles trapezoid. Properties of trapezoid: 1, and the upper bottom of trapezoid is parallel to the lower bottom; 2. The center line of the trapezoid is parallel to the two bottoms and equal to half of the sum of the upper and lower bottoms.