# SAT Math Multiple Choice Question 885: Answer and Explanation

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**Question: 885**

**15.** If, where *x* > 0 and *a* > 0, which of the following gives *a* in terms of *x*?

- A.
- B.
- C.
- D.

**Correct Answer:** A

**Explanation:**

**A**

**Difficulty:** Medium

**Category:** Passport to Advanced Math / Exponents

**Strategic Advice:** When a number (or a variable) is raised to a negative exponent, rewrite it as the reciprocal of the number with a positive exponent. You can also write fraction exponents as radicals to make using an inverse operation more recognizable.

**Getting to the Answer:** To write *a* in terms of *x*, you need to solve for *a*. To do this, you need to eliminate the fraction exponent, which also happens to be negative:

To eliminate the radical (the cube root), cube both sides of the equation:

Cross-multiply to get the *a* out of the denominator, and then divide both sides by *x*^{6}:

Choice (A) is correct.