SAT Math Multiple Choice Practice Question 388: Answer and Explanation
Line m (not shown) is the reflection of line l over the x-axis. What is the slope of line m?
Correct Answer: B
B Consider the points (0, 2) and (3, 0) on line l. When these points are reflected over the x-axis, (0, 2) transforms to (0, –2) and (3, 0) stays at (3, 0) because it is on the x-axis. You can then use the slope formula to find the slope of line m:
It's helpful to notice that whenever a line is reflected over the x-axis (or the y-axis, for that matter—try it), its slope becomes the opposite of the original slope.