
Use the formula for area of a triangle: \[ \text{Area} = \frac{1}{2} \times \text{side}_1 \times \text{side}_2 \times \sin(\text{included angle}) \] So, \[ \text{Area of } \triangle ADE = \frac{1}{2} \times AD \times AE \times \sin A \] Substituting values: \[ = \frac{1}{2} \times 2x \times 2y \times \sin A = 8 \] \[ \Rightarrow 2x \cdot 2y \cdot \frac{1}{2} \cdot \sin A = 8 \Rightarrow 2xy \cdot \sin A = 8 \Rightarrow xy \cdot \sin A = 4 \tag{1} \]
Again using the area formula: \[ \text{Area of } \triangle ABC = \frac{1}{2} \times AB \times AC \times \sin A \] Substituting values: \[ = \frac{1}{2} \times 3x \times 5y \times \sin A = \frac{15}{2} \cdot xy \cdot \sin A \] From equation (1), substitute \( xy \cdot \sin A = 4 \): \[ \text{Area} = \frac{15}{2} \cdot 4 = 30 \]
∴ Area of triangle \( ABC = 30 \)
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: