Nonlinear Functions

SAT Math· difficulty 4/5

If f(x)=x2+1f(x) = x^2 + 1 and f(g(x))=x24x+5f(g(x)) = x^2 - 4x + 5, what is g(x)g(x)?

  • A

    x+2x + 2

  • B

    2x42x - 4

  • C

    x2x - 2

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  • D

    x24x^2 - 4

Explanation

f(g(x))=g(x)2+1=x24x+5f(g(x)) = g(x)^2 + 1 = x^2 - 4x + 5, so g(x)2=x24x+4=(x2)2g(x)^2 = x^2 - 4x + 4 = (x - 2)^2. Thus g(x)=x2g(x) = x - 2.

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