Difference of squares formula
[tex]a^2-b^2=(a+b)(a-b)[/tex]
To find a and b in this case, we have to take the square root of the terms, as follows:
[tex]\begin{gathered} a=\sqrt[]{9k^4}=\sqrt[]{9}\sqrt[]{k^4}=3k^{\frac{4}{2}}=3k^2 \\ b=\sqrt[]{25}=5 \end{gathered}[/tex]
Substituting these values into the general formula:
[tex]9k^4-25=(3k^2+5)(3k^2-5)[/tex]
