A ladder is leaning against a wall, forming a 45-degree angl...

Question Analysis
This problem assesses the application of the cosine function in a real-world context involving a 45-45-90 triangle.

Key Concept Explanation
In a 45-45-90 triangle, the sides are in the ratio 1:1:√2, where the hypotenuse is √2 times the length of each leg.

Step-by-step Solution
1. Identify the given value: hypotenuse (ladder length) = 18 feet.
2. Use the cosine of 45 degrees:
3. Set up the equation: