How to answer it
- Evaluate each function value separately.
- Keep negative results in parentheses.
- Then combine as the question asks.
Worked example
An original question in the ACT format, already answered.
ACT MathWorked example
g(x) = x² − 4x
What is the value of g(5) − g(1)?
- A2
- B4
- C8
- D12
Answer: C. g(5) = 25 − 20 = 5 and g(1) = 1 − 4 = −3. Then 5 − (−3) = 8. Choice A subtracts 3 instead of −3.
The most common trap
Losing a negative sign when subtracting a negative value.
Practice it
Hourly Prep’s daily sets mix functions with the rest of ACT Math, and send more of it your way when it’s a weak spot. See how the ACT prep plan works, or browse the other ACT skill guides.
For pacing and strategy across the whole section, read our 2027 ACT format guide. To fit this skill into a schedule, see the ACT study plan guide.