Answer
(9r+1)(9r-1)
Work Step by Step
We use the formula for the difference of squares to apply to this question.
The difference of squares formula is:
$(a-b) (a+b) = a^{2} - b^{2}$
= $81r^{2}$ - 1
*** Take the square root of $81r^{2}$ which is 9r. Becuase 9r × 9r= $81r^{2}$
*** Take the square root of 1 which is 1. Becuase 1 × 1= 1
= $(9r)^{2}−1^{2}$
In the given formula let 9r represents a and 1 represents b.
$(9r)^{2}−1^{2}$ = (9r+1)(9r-1)
