ACT · Intermediate Algebra · Function notation and composition
Question act-q-00357
Easy Multiple choice No calculator
The question
If f(x) = 2x² + 5, what is the value of f(-2)?
- 13
- 14
- 1
- -13
Show answer & worked solution
Answer: 13
Worked solution. Substitute x = -2: f(-2) = 2 × (-2)² + 5 = 2 × 4 + 5 = 8 + 5 = 13.
Why each wrong choice is wrong. Forgetting to square the input is the dominant error — the linear-substitution distractor catches it.
Test-day tactic. Substitute with parentheses around the input. (-2)² always equals 4, regardless of the sign of -2.
About this question type
Items test substitution into function notation, composition, and (occasionally) inverse functions.
You will see a question shaped like this one on roughly every other official ACT form, typically at an early position in the section, where missing them carries an outsize penalty because the curve assumes everyone in your band gets them right. Treat any miss in this subtopic as a signal to drill the subtopic page before you do another full practice test.