SAT Math Multiple Choice Practice Question 525: Answer and Explanation

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Question: 525

3. Line l contains points (3, 2) and (4, 5). If line m is perpendicular to line l, then which of the following could be the equation of line m ?

A. y = -x + 3
B. y = - x + 5
C. y = -3x + 5
D. y = 5x +
E. y = 5x +

Correct Answer: B


B First, find the slope of line l by using the slope formula: . A line perpendicular to line l must have a slope that is the negative reciprocal of l's slope. So, its slope should be ?. In the standard line equation y = mx + b, m is the slope. Only B has a slope of ?. If you didn't remember the rule about the slope of perpendicular lines, you could have sketched out each of the lines and looked for the answer that looked perpendicular to l.

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