In any square, every two opposite sides are parallel and every two consecutive sides are perpendicular
Parallel lines have the same slope
The product of the slopes of the perpendicular lines is -1, which means if the slope of one m, then the slope of the other is (reciprocal m and change its sign)
The rule of the slope of the line which passes through the points (x1, y1) and (x2, y2) is m =
In square MNPR
∵ MN and NP are adjacent sides
∴ MN ⊥ NP
∵ M = (3, 8) and N = (-2, 1)
∴ x1 = 3 and y1 = 8
∴ x2 = -2 and y2 = 1
→ Use the rule of the slope above to find the slope of MN