AlgebraVery hardWhere one linear function is twice another
Algebra practice question
Functions f and g are defined by f(x) = 3x + 8 and g(x) = 2x − 1. For what value of x is f(x) equal to twice g(x)?
Answer: 10
3x + 8 = 2(2x − 1) = 4x − 2, so 10 = x.
Common wrong answers
- If you answered 9
- 9 comes from 3x + 8 = 2x − 1 doubled wrongly as 4x − 1: then x = 9.
- If you answered 38
- 38 is f(10), the common value of f and 2g, not x.
- If you answered -9
- −9 comes from 3x + 8 = 2x − 1 (forgetting to double g), giving x = −9.
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