PSAT Math Multiple-Choice Question 789: Answer and Explanation

Question: 789

A line has the equation y – 4x = 5. What is the slope of a line that is perpendicular to this line?

• A. -4
• B.
• C.
• D. 4

Correct Answer: B

Explanation:

(B) First, get this line in slope-intercept form so that you can easily identify the slope. You can do so by adding 4x to both sides to get:
y = 4x + 5
The slope of this line is 4. The slope of a line perpendicular to this one will have a slope that is the negative reciprocal, , which matches choice (B).