AlgebraVery hardFinding an input from a function defined by two points
Algebra practice question
For a linear function f, f(0) = 12 and f(4) = 0. For what value of x is f(x) = −6?
Answer: 6
Slope: (0 − 12)/(4 − 0) = −3, so f(x) = 12 − 3x. Then 12 − 3x = −6 gives 3x = 18, x = 6.
Common wrong answers
- If you answered 2
- 2 is where f(x) = 6, not −6.
- If you answered 18
- 18 is 3x, not x.
- If you answered -6
- −6 comes from solving 12 − 3x = 6 with a sign slip.
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