Rectangle Decomposition: Finding Triangle Units in a 14cm × 5cm Trapezoid

To solve this problem, we'll follow these steps:

• Step 1: Calculate the area of triangle KBC.
• Step 2: Determine the relevant dimensions for trapezoid AKCD and calculate its area.
• Step 3: Divide the area of the trapezoid by the area of the triangle to determine how many triangles fit into the trapezoid.

Now, let's work through each step:

Step 1: Calculate the area of triangle KBC.
KBC is a right triangle where $KB = 4 \, \text{cm}$ and $BC = 5 \, \text{cm}$ (since $AD = 5 \, \text{cm}$ is a vertical line segment in the rectangle, $BC$ must be equal to $AD$).
The area of triangle KBC is given by:

$\text{Area}_{KBC} = \frac{1}{2} \times \text{base} \times \text{height} = \frac{1}{2} \times 4 \times 5 = 10 \, \text{cm}^2$

Step 2: Calculate the area of trapezoid AKCD.
For trapezoid AKCD, $AK$ is the shorter parallel side, and $DC = 14 \, \text{cm}$ is the longer parallel side. The height is the same as the height of rectangle AD or BC, $h = 5 \, \text{cm}$.
To find $AK$, since $KB = 4 \, \text{cm}$ and total $AB = 14\, \text{cm}$, thus $AK = AB - KB = 14 - 4 = 10\, \text{cm}$.
The area of trapezoid AKCD is given by:

$\text{Area}_{AKCD} = \frac{1}{2} \times (AK + DC) \times h = \frac{1}{2} \times (10 + 14) \times 5 = \frac{1}{2} \times 24 \times 5 = 60 \, \text{cm}^2$

Step 3: Calculate how many triangles KBC fit into trapezoid AKCD.
To find how many triangles fit into the trapezoid, divide the area of trapezoid by the area of the triangle:

$\frac{\text{Area}_{AKCD}}{\text{Area}_{KBC}} = \frac{60}{10} = 6$

Therefore, the solution to the problem is that 6 triangles identical to triangle KBC are needed to create the trapezoid AKCD.