Geometry

Question Analysis:
This question tests knowledge of special right triangle properties, specifically the 45-45-90 triangle ratio.  
The main focus is applying the constant ratio between legs and hypotenuse in these triangles.

Key Concept Explanation:
In a 45-45-90 triangle:
- Two legs are equal (x)
- Hypotenuse is x√2
- This comes from applying the Pythagorean Theorem to two equal sides

Step-by-Step Solution:
1. Given: leg = 7 cm
2. Apply 45-45-90 ratio:
  hypotenuse = leg × √2
3. Calculate:
  7 × √2 = 7√2 cm

Common Mistakes:
1. Confusing with 30-60-90 triangle ratios