AlgebraEasy–MediumEvaluating a linear function from its rule
Algebra practice question
The function f is defined by f(x) = 4x + 9. What is the value of f(6)?
Answer: 33
Substitute x = 6: f(6) = 4(6) + 9 = 24 + 9 = 33.
Common wrong answers
- If you answered 19
- You added 4 + 6 + 9. The rule means multiply x by 4 first: 4(6) + 9 = 33.
- If you answered 24
- You multiplied 4 · 6 = 24 but never added the 9. f(6) = 24 + 9 = 33.
- If you answered 54
- You multiplied 6 by 9. The input multiplies the coefficient 4: f(6) = 4 · 6 + 9 = 33.
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