Final answer:
The condition that verifies that the triangle DEF is a right triangle is that the product of the slopes of two of its sides is -1.
Step-by-step explanation:
In order to verify that the triangle △DEF is a right triangle, we can check if the product of the slopes of two of its sides is -1.
We will calculate the slopes of the sides DE and EF using the formula: slope = (y2 - y1) / (x2 - x1).
The slope of DE is (5 - 2) / (2 - (-2)) = 3/4, and the slope of EF is (1 - 5) / (5 - 2) = -4/3.
The product of these slopes is (3/4) * (-4/3) = -1. Since the product is -1, the condition is verified and △DEF is a right triangle. The answer is option D.