Factorize the expressions: i) X2 - 11X + 30 ii) 25X2 - 9

The expression is $X^2 - 11X + 30$. We need to find two numbers that multiply to 30 and add up to $-11$. These numbers are $-5$ and $-6$.

The factorization for part i is $\boxed{(X - 5)(X - 6)}$.

The expression is $25X^2 - 9$. This is in the form of a difference of squares, $a^2 - b^2 = (a - b)(a + b)$.
Here, $a^2 = 25X^2$, so $a = \sqrt{25X^2} = 5X$.
And $b^2 = 9$, so $b = \sqrt{9} = 3$.

The factorization for part ii is $\boxed{(5X - 3)(5X + 3)}$.