To find the x-intercept(s) of the function \( f(x) = 9x^2 - 81 \), we need to set \( f(x) \) equal to zero and solve for \( x \):
\[ 9x^2 - 81 = 0 \]
Next, we can add 81 to both sides:
\[ 9x^2 = 81 \]
Now, divide both sides by 9:
\[ x^2 = 9 \]
Now, take the square root of both sides:
\[ x = \pm 3 \]
Thus, the x-intercepts of the function are:
\[ x = 3 \quad \text{and} \quad x = -3 \]
In conclusion, the x-intercepts are:
\[ x = 3 \quad \text{and} \quad x = -3 \]