To factor the quadratic expression \( x^2 - 9x + 18 \), we will look for two numbers that multiply to the constant term (18) and add up to the coefficient of the linear term (-9).
The factors of 18 that sum to -9 are -6 and -3.
Thus, we can factor the expression as follows:
\[ x^2 - 9x + 18 = (x - 6)(x - 3) \]
So, the factored form of \( x^2 - 9x + 18 \) is:
\[ (x - 6)(x - 3) \]