How can I determine the value of x that will make the expression a real

√x-1

The content of the square root must be greater than or equal to zero. Determine the conditions on x that make this true.

As written, you require

... x ≥ 0

If you intend

... √ (x - 1) ∈ ℝ

Then

... x - 1 ≥ 0

Solve this inequality by adding 1.

... x ≥ 1