# How do you factor 9t^2-1 ?

I think you mean $9 {t}^{2} - 1$, in which case the answer is:
$9 {t}^{2} - 1 = {\left(3 t\right)}^{2} - {1}^{2} = \left(3 t - 1\right) \left(3 t + 1\right)$
${a}^{2} - {b}^{2} = \left(a - b\right) \left(a + b\right)$