SAT Math Multiple Choice Practice Question 388: Answer and Explanation

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Question: 388


Line m (not shown) is the reflection of line l over the x-axis. What is the slope of line m?

A. 3/2
B. 2/3
C. 0
D. -2/3
E. -3/2

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.

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