Final answer:
Beverly can use the slopes of line segments PQ and QR to show that △PQR is a right triangle, as their slopes are negative reciprocals which prove perpendicularity.
Step-by-step explanation:
Beverly can prove that △PQR is a right triangle by calculating the slopes of two of the sides and showing that they are perpendicular by means of their slopes being negative reciprocals of each other. The slope of the line segment PQ can be calculated using the coordinates P(-2, 5) and Q(-1, 1), and the slope of the line segment QR can be calculated using the coordinates Q(-1,1) and R(7, 3).
The slope of PQ is found by the formula slope = (y2 - y1) / (x2 - x1), which gives us (1 - 5) / (-1 - (-2)) = -4 / 1 = -4. Similarly, the slope of QR is (3 - 1) / (7 - (-1)) = 2 / 8 = 1/4. Since the slopes are negative reciprocals (-4 and 1/4), this indicates that PQ and QR are perpendicular, thus confirming that △PQR is a right triangle.