SAT Math Multiple Choice Practice Question 179: Answer and Explanation

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Question: 179

3. Line j intersects line k at a 90° angle. If the equation of line j is , which of the following could be the equation of line k?

E. y = 3x + 4

Correct Answer: C


C. If j and k intersect at a 90-degree angle, then they are perpendicular. You may remember that perpendicular lines have slopes that are opposite reciprocals. (See Chapter 14 to brush up on reciprocals.) The slope of j is , and the opposite reciprocal of is . So for line k, you're looking for a line with a slope of , and Choice (C) is the only option with that slope.

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