ANSWER
(x + 15)(x - 15)
EXPLANATION
The difference of squares is equivalent to the product of the sum and subtraction of the bases,
[tex]a^2-b^2=(a+b)(a-b)[/tex]
So, to factor this difference of squares, we have to find the principal square roots of each term,
[tex]\begin{gathered} \sqrt[]{x^2}=x \\ \sqrt[]{225}=15 \end{gathered}[/tex]
So this is,
[tex]x^2-225=x^2-15^2=(x+15)(x-15)[/tex]
Hence, the factored form is (x + 15)(x - 15).
