Answer :

use formula^:   a²-b²= (a-b)(a+b)
x²-1=0

x²-1²=0
(x-1)(x+1)=0
x-1=0⇒ x₁=-1
x+1=0 ⇒x₂=1
Answer: x=+-1
x² - 1 = 0
   + 1  + 1
      x² = 1
       x = +1