PSAT Math Multiple-Choice Question 668: Answer and Explanation

Question: 668

What is the vertex of the parabola (y - 4)² = 17(x + 2)?

• A. (-2, 4)
• B. (2, -4)
• C. (-4, 2)
• D. (4, -2)

Correct Answer: A

Explanation:

(A) This equation is probably a bit different from the equations of the parabolas that you're used to seeing. To get it into standard form, we need to solve for x instead of the y as we usually do:

This is a parabola rotated 90 degrees clockwise. The standard form can be represented by the equation:

x = a(y - k)² + h

Therefore, in this problem, k = 4 and h = -2. So (h, k) is (-2, 4), as shown in choice (A). Parabola problems like this may not be on the PSAT, but it is included here so that you will be as prepared as possible.