SAT Math Multiple Choice Practice Question 95: Answer and Explanation

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Question: 95

7. Two lines in the coordinate plane, l and m, pass through the point (3, 4). Line l also passes through (5, 8). If line m is perpendicular to line l, then line m also passes through

A. (0, 0)
B. (1, 5)
C. (1, 8)
D. (5, 0)
E. (8, 5)

Correct Answer: B


B. I'd start by making a quick sketch:

Perpendicular lines have slopes that are negative reciprocals, so first find the slope of l: . That means line m has a slope of -1/2. Now you can just put some of the given points on the line by counting spaces on improvised graph paper (draw your own lines), or you can try plugging the answer choices into the slope formula, in which case plugging in Choice (B) gives you .

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