SAT Math Multiple Choice Practice Question 122: Answer and Explanation

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Question: 122

12. A function is defined by . For

what value(s) of x would the function equal 25?

A. 12.5 only
B. 12.5 or
C. 81 only
D. 81 or -81
E. none of the above

Correct Answer: C


C. Don't plug in 25 for x; you want the whole function to equal 25. So, , and must equal 4. Therefore, equals 9, which is true when x = 81.

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