To determine the end behavior of the function \( f(x) = 3(x - 3)(x^2 + 3) \), we can analyze the degrees of the polynomial.
- The function is a product of a linear term \( (x - 3) \) and a quadratic term \( (x^2 + 3) \).
- The degree of \( (x - 3) \) is 1, and the degree of \( (x^2 + 3) \) is 2.
- Therefore, the overall degree of \( f(x) \) is \( 1 + 2 = 3 \), meaning it is a cubic polynomial.
- Since the leading coefficient (from the term \( 3 \)) is positive, we know how the ends of the graph behave based on the degree.
- For a cubic polynomial with a positive leading coefficient, the end behavior is:
- As \( x \to -\infty \) (left side), \( f(x) \to -\infty \).
- As \( x \to +\infty \) (right side), \( f(x) \to +\infty \).
Based on this analysis, the correct choice is:
D. Down on the left side, up on the right side.