Geometry

Question Analysis:
This question uses diagonal congruence to identify a rectangle.
The main focus is using diagonal expressions to form an equation.

Key Concept Explanation:
In a rectangle, diagonals are always congruent.

Step-by-Step Solution:
Set AC = BD: 5x − 1 = 2x + 8 → 3x = 9 → x = 3

Option Analysis:
Only C satisfies the condition of equal diagonal...