Answer:
[tex](k+9)(k-9)[/tex]
Step-by-step explanation:
[tex]k^2-81[/tex]
[tex]k^2-9^2[/tex]
Apply the difference of squares formula: [tex]x^2-y^2=\left(x+y\right)\left(x-y\right)[/tex]
Thus, [tex]k^2-9^2=\left(k+9\right)\left(k-9\right)[/tex]
