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