Proof Wide Formula Trapezoid

Trapezoid is a rectangle that has a proper pair of parallel sides. Trapezoid comprehensive formula we already know when the elementary schools, but few of us know where it comes from this formula, because when only a primary school using the formula. This article will discuss how this Trapezoid Wide Formula derivatives. In this derivation, I will use three cases of shape (picture) Trapezoid.

1. Trapesium 1
   
   In this first Trapezoid, I consider that the Trapezoid consists of a rectangle and two triangles are the same.
   LTrapesium = Size Rectangle + 2 Size Triangle
   = (a x t) + (1/2 x c x t)
   = (1/2 x 2a x t) + (1/2 x c x t) + (1/2 x c x t)
   = 1/2 x t x (2a + c + c)
   because (2a + c + c) is the number of sides that are parallel, resulting in
   = 1/2 x height x number of sides are parallel
2. Trapesium 2
   
   Then in the second Trapezoid, I saw that the wake Trapesiumini consists of a rectangle and two triangles are different.
   LTrapesium = Size Rectangle + Size Triangle 1 + Size Triangle 2
   = (a x t) + (1/2 x b x t) + (1/2 x c x t)
   = (1/2 x 2a x t) + (1/2 x b x t) + (1/2 x c x t)
   = 1/2 x t x (2a + b + c)
   because (2a + b + c) is the number of sides that are parallel, resulting in
    
   = 1/2 x height x number of sides are parallel
3. Trapesium 3
   
   Then on the last Trapezoid, I saw that the wake Trapezoid consists of a rectangle and a triangle.
   LTrapesium = Size Rectangle + Size Triangle
   = (a x t) + (1/2 x c x t)
   = (1/2 x 2a x t) + (1/2 x c x t)
   = 1/2 x t x (2a + c)
   because (2a + c) is the number of sides that are parallel, resulting in
        = 1/2 x height x number of sides are parallel
   
   Wide Formula Trapezoid = 1/2 x height x number of sides are parallel

Source