Solve `(x^2-4)sqrt(x^2-1)<0.`

Explanation

`(x^2-4)sqrt(x^2 -1) lt 0.`
We must have `x^2- 1 ge 0 `
or `x^2 ge 1`
or `x le - 1 or x ge 1`
Also `(x^2-4)sqrt(x^2-1) lt 0`
or `x^2-4 gt 0`
or `x^2 lt 4`
Or `-2 lt x lt 2`
From (1) and (2) we have `x in (-2, -1] cup [1,2)`