Answer:
x = 1
Explanation:
f(x) = x² - 1
to solve let f(x) = 0 , then
x² - 1 = 0 ← x² - 1 is a difference of squares and factors in general as
a² - b² = (a + b)(a - b)
x² - 1 = 0
x² - 1² = 0
(x + 1)(x - 1) = 0 ← in factored form
equate each factor to zero and solve for x
x + 1 = 0 ⇒ x = - 1
x - 1 = 0 ⇒ x = 1
solutions are x = - 1 ; x = 1