What is the slope of a line perpendicular to the line y = 3x + 4?

• A. 3
• B. -1/3
• C. 1/3
• D. -3

Answer: (B)

When two lines are perpendicular, their slopes multiply to -1. So the slope of a line perpendicular to one with slope 3 is the negative reciprocal of 3, which is -1/3. This ensures 3 × (-1/3) = -1, confirming perpendicularity. The value -1/3 matches the correct choice. The other options would not give the necessary product of -1 (for example, 3 would be parallel, 1/3 is positive, and -3 would not yield -1 when multiplied by 3).