Digital PSAT Math Practice Question 158: Answer and Explanation

Question: 158

If f(a) = a² - 12, what is f(b - a)?

• A. a² + b² - 12
• B. a³ - b - 12
• C. a² - 2ab - b² - 12
• D. a² - 2ab + b² - 12

Correct Answer: D

Explanation:

(D) Just plug in (b - a) wherever there is an a in the expression for f (a):

Next, use FOIL for (b - a)²:

Plug this back into f(b - a):

This can be arranged as f(b - a) = a² - 2ab + b² -12, choice (D).