To express \( 216^{-\frac{1}{3}} \) using rational exponents, we first note that \( 216^{-\frac{1}{3}} \) can be written as:
\[ \frac{1}{216^{\frac{1}{3}}} \]
The expression \( 216^{\frac{1}{3}} \) denotes the cube root of 216. Therefore, the expression \( 216^{-\frac{1}{3}} \) represents the reciprocal of the cube root of 216.
Thus, the rational exponent in the expression \( 216^{-\frac{1}{3}} \) is \( -\frac{1}{3} \).
So the correct answer is:
−\(\frac{1}{3}\) or negative Start Fraction 1 over 3 End Fraction.