We start with the polynomial expression \( x^{2} - 12x + 27 \). To factor this expression, we look for two numbers that multiply to \( 27 \) (the constant term) and add up to \( -12 \) (the coefficient of the linear term).
Step 2: Identify the Factors
The numbers that satisfy these conditions are \( -9 \) and \( -3 \). Therefore, we can express the polynomial as:
\[
x^{2} - 12x + 27 = (x - 9)(x - 3)
\]
Final Answer
The factorized form of the polynomial \( x^{2} - 12x + 27 \) is:
\[
\boxed{(x - 9)(x - 3)}
\]