f(x) = 4x^2 - 3. sqrt(3)
Set this equal to 1 first, and solve for x: 4x^2 = 3, and x^2 =3/4, so
sqrt(3)
x = -----------
2
This is approx. 0.866. It's the lower end of the domain.
Set f(x) = 13 to find the higher end of the domain: 4x^2 - 3 = 13
Simplifying, 4x^2 = 16, x^2 = 4, and x=2
The domain here does not include the end points sqrt(3) / 2 or 2; it is
( sqrt(3) / 2, 2) (answer)