Geometry

Question Analysis:
This problem examines understanding of coordinate reflection across the diagonal line y = -x, specifically applied to geometric shapes.
Students must correctly apply the reflection transformation to each vertex.

Key Concept Explanation:
Reflection across y = -x follows the transformation rule: (x, y) → (-y, -x).
This operation swaps the coordinates and changes both signs.
For geometric figures, each vertex must undergo this transformation individually.

Step-by-Step Solution:
Original vertex C: (4, 6)
Apply reflection rule: swap coordinates → (6, 4)
Change both signs → (-6, -4)
Therefore, C' = (-6, -4)

Common Mistakes:
Swapping coordinates but forgetting to negate them
Confusing y = -x with y = x reflection (which only swaps coordinates)
Applying ...