Algebra practice question

Answer: 3

f(f(x)) = m(mx + b) + b = m²x + (m + 1)b. So m² = 4, m = 2 (since m > 0), and 3b = 9 gives b = 3.

Common wrong answers

If you answered 9

9 is the constant of f(f(x)), not of f.

If you answered -9

−9 corresponds to m = −2, which is ruled out.

If you answered 4.5

4.5 divides 9 by m instead of by m + 1.

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