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If \( f(x) = x - 1 \), and \( g(f(x)) = 3 + 2x - x^2 + x^3 \), which of the following gives a correct expression for \( g(x) \)?

Question and options

If f(x)=x−1 f(x) = x - 1 , and g(f(x))=3+2x−x2+x3 g(f(x)) = 3 + 2x - x^2 + x^3 , which of the following gives a correct expression for g(x) g(x) ?
  1. x3−4x2+7x−4x^3 - 4x^2 + 7x - 4
  2. x3+2x2+3x+5x^3 + 2x^2 + 3x + 5
  3. x3−2x2+3x−5x^3 - 2x^2 + 3x - 5
  4. x3+2x2+3x+3x^3 + 2x^2 + 3x + 3

Answer and explanation

Correct answer: B - \(x^3 + 2x^2 + 3x + 5\)
Let t = x - 1, so x = t + 1. g(t) = 3 + 2(t+1) - (t+1)^2 + (t+1)^3 = t^3 + 2t^2 + 3t + 5.

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