$(3 x-1)^{2}$

Step 1 ：Apply the binomial theorem to expand the expression: $(3x - 1)^2 = \binom{2}{0}(3x)^2(-1)^0 + \binom{2}{1}(3x)^1(-1)^1 + \binom{2}{2}(3x)^0(-1)^2$

Step 2 ：Simplify the expression: $(3x - 1)^2 = 9x^2 - 6x + 1$

Step 3 ：The expanded form of the given expression is \(\boxed{9x^2 - 6x + 1}\)