What is the minimum value of $f(x) = 9x^2 + 6x + 4$?

Explanation

1. 01

   Complete the square: $9x^2 + 6x + 4 = (3x + 1)^2 + 3$.

2. 02

   The square is least, 0, at $x = -\frac{1}{3}$, so the minimum value is 3.