For this case we have a difference of perfect squares of the form:
[tex]a ^ 2-b ^ 2 = (a + b) (a-b)[/tex]
Applying to the given exercise we have to:
[tex]a = 7x\\b = 9[/tex]
So, we have:
[tex]49x ^ 2-81 =\\(7x) ^ 2- (9) ^ 2 =\\(7x + 9) (7x-9)[/tex]
Thus, the factorization of [tex]49x ^ 2-81[/tex] is given by:
[tex](7x + 9) (7x-9)[/tex]
Answer:
[tex](7x + 9) (7x-9)[/tex]
