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Linear Functions

SAT Math· difficulty 5/5

For the linear function ff, f(2x)=6x+5f(2x) = 6x + 5 for all xx. What is f(7)f(7)?

  • A

    26

    check_circle
  • B

    23

  • C

    47

  • D

    21

Explanation

Let u=2xu = 2x, so x=u/2x = u/2. Then f(u)=6(u/2)+5=3u+5f(u) = 6(u/2) + 5 = 3u + 5. So f(7)=21+5=26f(7) = 21 + 5 = 26.

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