PSAT Math Multiple-Choice Question 438: Answer and Explanation

Question: 438

y² = 2x² - 8x + c

The quadratic above has only one distinct, real root. What is the value of c ?

• A. -8
• B. -4
• C. 4
• D. 8

Correct Answer: D

Explanation:

D

Difficulty: Medium

Category: The Quadratic Formula

Getting to the Answer: In order for the quadratic to have only one root, the discriminant must be equal to 0. Plug the numbers given into the discriminant, set it equal to 0, and solve for c:

Therefore, (D) is correct.