A trapezoid is a quadrilateral with only a set of parallel opposite sides. Two parallel sides are called the bottom of the trapezoid, the lower and longer bottom is called the lower bottom, and the higher and shorter bottom is called the upper bottom. 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. Isosceles trapezoid, called isosceles trapezoid, is a special trapezoid, and its judgment method is similar to isosceles triangle. Trapezoids are unstable.
The derivation process of trapezoidal area formula;
Derived from parallelogram, because the area of parallelogram row is: base x height /2. Then two completely equal trapezoids can be spliced into a parallelogram, and the bottom of the spliced parallelogram is the upper bottom plus the lower bottom of the trapezoid, and the height is unchanged. Then the area of a trapezoid is required to be /2 of the area of the spliced parallelogram, from which it can be deduced that: S ladder = (upper bottom+lower bottom) * height /2.