
We are given a composite figure consisting of a rectangle and an isosceles triangle.
Step 1: Drop a perpendicular $DE$ from point $D$ onto line $AB$.
This divides the figure into two parts:
Step 2: Calculate the area of the rectangle:
$\text{Area of rectangle} = \text{length} \times \text{breadth} = 5 \times 4 = 20 \;\text{cm}^2$
Step 3: Calculate the area of the triangle $AED$:
$\text{Area of triangle} = \frac{1}{2} \times \text{base} \times \text{height} = \frac{1}{2} \times 4 \times 4 = 8 \;\text{cm}^2$
Step 4: Add both areas to get the total area:
$\text{Total area} = 20 + 8 = 28 \;\text{cm}^2$
∴ Required Area = $28 \;\text{cm}^2$
For any natural number $k$, let $a_k = 3^k$. The smallest natural number $m$ for which \[ (a_1)^1 \times (a_2)^2 \times \dots \times (a_{20})^{20} \;<\; a_{21} \times a_{22} \times \dots \times a_{20+m} \] is: