Worked example 1
Let f(x) = 3x² + 6x − 6. Find f(4).
Remember: Replace every x by 4.
- f(4) = 3 × 4² + 6 × 4 − 6.
- 4² = 16, so the first term is 3 × 16 = 48 and the second is 24.
- f(4) = 66.
Use function notation to find the value of a function
Follow this one with me, a step at a time. Try to guess each step first.
Common mistakes
- Multiplied by the coefficient and then squared. The index applies only to x.
- Read the square as multiplying by 2. A square means the number multiplied by itself.
- Left out the constant term.
One at a time. A wrong answer gets a second try, so have a go.
Question 1
Let f(x) = 3x² − x − 8. Find f(−2).
Question 2
Let f(x) = 2x² + x − 2. Find f(−4).
Question 3
Let f(x) = 2x² − 4x + 8. Find f(−4).
Topic quiz
Five questions on this topic, marked at the end. No hints and no answers along the way — that is what makes the result mean something.
Take the topic quiz