SAT Math Multiple Choice Practice Question 209: Answer and Explanation
11. If f(x) = x2 - 3x + 1, then f(2x) = ?
A. 2x2 - 3x + 1
B. 2x2 - 6x + 2
C. 4x2 - 3x + 1
D. 4x2 - 6x + 1
E. 2x3 - 6x2 + 2x
Correct Answer: D
D. When you see function notation, the first thought that pops into your head should be about substitution. In other words, f(x) tells you the rule to follow, no matter what's put inside of those parentheses. So, f(2x) tells you to replace every x in the original equation with 2x: f(2x) = (2x)2 - 3(2x) + 1. You can simplify this to Choice (D) if you use PEMDAS (covered in Chapter 12)!