Nonlinear Functions

SAT Math· difficulty 4/5

If f(x)=2x+1x3f(x) = \frac{2x + 1}{x - 3}, what is f1(x)f^{-1}(x)?

  • A

    x32x+1\frac{x - 3}{2x + 1}

  • B

    x12x+3\frac{x - 1}{2x + 3}

  • C

    2x1x+3\frac{2x - 1}{x + 3}

  • D

    3x+1x2\frac{3x + 1}{x - 2}

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Explanation

Swap and solve: x=2y+1y3x(y3)=2y+1xy2y=3x+1y=3x+1x2x = \frac{2y + 1}{y - 3} \Rightarrow x(y - 3) = 2y + 1 \Rightarrow xy - 2y = 3x + 1 \Rightarrow y = \frac{3x + 1}{x - 2}.

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