Question

domain of square root of 5x-20

Answer 1

The domain of this equation can be expressed as
\[\sqrt{5x-20} \ge0\]
Therefore, @sbarthole ?

Answer 2

It's a tautology to say \[
\sqrt{f(x)}\geq 0
\]When \(f(x)\in\mathbb R\).

Answer 3

It's a positive square root.

What you wanna check is that \[
5x-20\geq 0
\]

Answer 4

Thanks for emphasizing @wio.