10. A rectangle whose length is twice its width has a diagonal equal to one side of a given square. The ratio of the area of the rectangle to the area of the square is​

2/5

Step-by-step explanation:

First, we can draw the rectangle out, as shown. The length is twice the width, and the diagonal, y, cuts across the rectangle. This forms a right triangle, and using the Pythagorean Theorem, we can say that

y² = x² + (2x)²

y² = x² + 4x²

y² = 5x²

square root both sides

y=√(5x²)

The diagonal, or y, is equal to √(5x²). This is equal to one side of the square

The area for the rectangle, which we need to find for the ratio, is length * width = x * 2x = 2x²

The area for the square, which we also need to find for the ratio, is (side length)² = √(5x²) = 5x²

The ratio for the area of the rectangle to the area of the square is therefore 2x²/5x² = 2/5 (crossing out the x² in both the numerator and the denominator). We know to put the rectangle on top because of the specific wording of "the ratio of the area of the rectangle to..."