Triangle LMN is reflected across a line, L = (12, –7), and L’ = (–7, 12). What is the line of reflection?

A reflection across the line y = x switches a point’s coordinates: (x, y) becomes (y, x). The point L = (12, −7) therefore maps to (−7, 12), which is L’. So the line of reflection is y = x, choice C.

AI-written and checked against the verified answer.