Question

Triangle ABC has been rotated 90° to create triangle DEF. Using the image below, prove that perpendicular lines have opposite and reciprocal slopes. You must show all of your work to receive credit.

Triangles ABC and DEF are shown. A is at 4, 2. B is at 4, 5. C is at 1, 2. D is at 2, negative 4. E is at 5, negative 4. F is at 2, negative 1. Line BC and line EF intersect at point 0, 1.