What is the factored form of the expression?

16b^2 - 81

(4b-9) (4b+9)

Step-by-step explanation:

16b^2 - 81

This is the difference of squares

(a^2 - c^2) = (a-c) (a+c)

a^2 = 16b^2 so a = 4b

c^2 = 81 so c = 9

(16b^2 - 81) = (4b-9) (4b+9)