Geometry

Question Analysis:
This problem uses the Pythagorean Theorem in a rectangle.
The main focus is finding diagonal from side expressions.

Key Concept Explanation:
In a rectangle, diagonal = √(side₁² + side₂²)

Step-by-Step Solution:
Diagonal = √[(2x)² + x²] = √(4x² + x²) = √5x² = x√5

Common Mistakes:
Forgetting to square the sides
Misapplying sq...