The slope of one of the dotted lines is equal to: 1.
The slope of the reflection line is equal to: -1.
The following mathematical equation can be used in geometry and mathematics to find the slope of any straight line:
Slope (m) is equal to (y-axis change, Δy) / (x-axis change, Δx).
Rise/run = slope (m)
slope (m) =

The slope of one of the dotted lines can be found by entering the provided data points (-5, 6) and (-2, 9) into the formula for line slope.
m = (9 - 6)/(-2 + 5) is the slope.
Slope (m) equals 1/3
Slope (m) is equal to 1.
The slope of the reflection line can be found by using the given data points (-5, 6) and (-4, 5) as substitutes in the slope of a line formula.
m = (5 - 6)/(-4 + 5) is the slope.
Slope (m) equals -1/1.
Slope (m) is equal to -1