1. **Stating the problem:** We are asked to write the algebraic expression for the ratio of the area of square EFGH to the area of rectangle ABCD. 2. **Identify the areas:** - The rectangle ABCD has sides AB = $y$ and AD = $2x$, so its area is $$\text{Area}_{ABCD} = y \times 2x = 2xy.$$ - The square EFGH has side length $x$, so its area is $$\text{Area}_{EFGH} = x^2.$$ 3. **Write the ratio of the areas:** $$\text{Ratio} = \frac{\text{Area}_{EFGH}}{\text{Area}_{ABCD}} = \frac{x^2}{2xy}.$$ 4. **Simplify the fraction:** We can cancel $x$ from numerator and denominator: $$\frac{\cancel{x} \times x}{2y \times \cancel{x}} = \frac{x}{2y}.$$ 5. **Final simplified expression:** $$\boxed{\frac{x}{2y}}.$$ 6. **Identify numerator and denominator:** - Numerator (tử thức) is $x$. - Denominator (mẫu thức) is $2y$. This completes the problem.