ACT · Elementary Algebra · Substitution and evaluation
Question act-q-00311
Medium Multiple choice No calculator
The question
If f(x) = 2x² + 3, what is the value of f(6)?
- 76
- 75
- -75
- 15
Show answer & worked solution
Answer: 75
Worked solution. Substitute x = 6: f(6) = 2 × (6)² + 3 = 2 × 36 + 3 = 72 + 3 = 75.
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. (6)² always equals 36, regardless of the sign of 6.
About this question type
A value or set of values is given for the variables; substitute and compute. The arithmetic can be tricky when negatives or fractions are involved.
You will see a question shaped like this one on roughly every other official ACT form, typically at a moderate position in the section — solidly within the range that separates a 600-band student from a 700-band student. Treat any miss in this subtopic as a signal to drill the subtopic page before you do another full practice test.