Factor 9sec(a)^2-9tan(a)^2

$9 \sec^{2} (a) - 9 \tan^{2} (a)$

Factor $9$ out of $9 \sec^{2} (a) - 9 \tan^{2} (a)$ .

Factor $9$ out of $9 \sec^{2} (a)$ .

$9 (\sec^{2} (a)) - 9 \tan^{2} (a)$

Factor $9$ out of $- 9 \tan^{2} (a)$ .

$9 (\sec^{2} (a)) + 9 (- \tan^{2} (a))$

Factor $9$ out of $9 (\sec^{2} (a)) + 9 (- \tan^{2} (a))$ .

$9 (\sec^{2} (a) - \tan^{2} (a))$

Apply pythagorean identity.

$9 \cdot 1$