[tex]\mathsf{Given \ function \ is : 2\sqrt{x - 6}}[/tex]
We can see that there is a square root in the function.
As the value inside the square root should always be positive, We can conclude that (x - 6) should always be positive and can also be equal to zero.
[tex]\implies \mathsf{x - 6 \geq 0}[/tex]
[tex]\implies \mathsf{x \geq 6}[/tex]
[tex]\implies \mathsf{6 \ \leq \ x \ < \ \infty}[/tex]
