This is similar to Problem 4 from your Section 4.3 worksheet.

Factor.

$x^2-81 = \big($ $\big) \big($ $\big)$

$9 m^2 - 49 = \big($ $\big) \big($ $\big)$

$4 a^2-25 b^2 = \big($ $\big) \big($ $\big)$

Hint: