need to explain

Note, √( 1 - 1/x^2)  =

√(x^2 - 1) * 1 / √(x^2)

But, by the absolute value property  1 / √(x^2) = 1 / l x l  because  x could  be negative

Therefore,

(1/ √(x^2)) * x^2  =  (1 / l x l ) * x^2  .... and x^2  = √(x^2) * √(x^2) = l x l * l x l

So, we end up with

l x l * l x l / l x l   =  l x l

And, of course, this is multiplied by √(x^2 - 1)