PSAT Math Multiple-Choice Question 24: Answer and Explanation

Question: 24

If y = 6x + 3 and y = cx + 3 are the equations of perpendicular lines, then what is the value of c?

• A. -6
• B.
• C.
• D. 6

Correct Answer: B

Explanation:

B

The question asks for the value of a constant in one of the two given equations. The slope-intercept form of the equation of a line is y = mx + b, where m is the slope and b is the y-intercept. So, the slope of the line given by the first equation is 6. The question states that the two equations are of perpendicular lines. To find the slope of a perpendicular lines, which have slopes that are negative reciprocals of each other. The equation of the second line is also in slope-intercept form, so c is the slope. Take the negative reciprocal of 6 to find that c = -. The correct answer is (B).