Factor 81 - a^2.......

This is the difference of two squares: (9)^2 - a^2 = (9 + a)(9 - a)

Have you heard of the difference of two squares?

Basically, a^2 - b^2 is the same as (a - b)(a + b). You can confirm this by multiplying out the brackets.

81 is 9 squared, so 81 - a^2 = (9 - a)(9 + a).

Recall 81 = 9^2

Expression becomes 9^2 - a^2 which is the difference of perfect squares

81 - a^2= 9^2 - a^2= (9+a)(9- a)

9² - a² = (9 - a)(9 + a)

9^2-a^2
(9+a)(9-a) because a^2-b^2=(a+b)(a-b)

(9-a)(9+a)

idk

umm...what's your question?