1. The formula of the circumference of the trapezoid is: upper bottom+lower bottom+waist+waist, expressed in letters: A+B+C+D.
2. The circumference formula of isosceles trapezoid is: upper bottom+lower bottom +2 waist, and the area is expressed by letters: a+b+2c.
3. The area formula of trapezoid is (upper bottom+lower bottom) × height ÷ 2, which is expressed in letters: S=(a+b)×h÷2.
4. Deformation1:h = 2s \ u (a+b); Variant 2: a = 2s ÷ h-b; Variant 3: b = 2s ÷ h-a.
5. another formula for calculating trapezoidal area: midline × height, expressed in letters: l h.
6. The area of trapezoid with mutually perpendicular diagonals is: diagonal x diagonal ÷2.
Trapezoids are divided into general trapeziums and special trapeziums. Special trapezoid is divided into isosceles trapezoid and right trapezoid. A quadrilateral with two parallel bases, two equal waists and non-parallel waists is called an isosceles trapezoid. The diagonal lines of isosceles trapezoid are equal, and the upper and lower bottom angles are equal respectively. The sum of an upper base angle and a lower base angle is 180 degrees, which are complementary. The isosceles trapezoid is an axisymmetric figure.
Extension:
Trapezoid is geometry knowledge in primary school mathematics. A set of quadrangles with parallel opposite sides is called trapezoid. Divided into isosceles trapezoid, right trapezoid and arbitrary trapezoid. It has four sides, four corners, four vertices and a set of parallel opposite sides. In primary school, we should correctly understand trapezoid and several special trapezoid, master the method of ladder height and the calculation method of trapezoid area.
Calculation method of height:
1 and the height can be calculated according to the perimeter, area and angle of the trapezoid.
2. If the conditions are not well understood, you can take the auxiliary line to help answer the questions. For example, draw auxiliary lines to form special shapes, such as equilateral triangle, right triangle and isosceles triangle.
3, or directly calculate the high value according to special calculation methods such as the Olympic number. The square of trapezoidal height = the square of trapezoidal bus (half of the difference between the upper and lower parallel bottoms). Note that if it is a right-angled trapezoid, the square of the trapezoid height = the square of the trapezoid bus (the difference between the upper and lower parallel bases).