y = sqrt( x-4)
The domain is the value that x can take
sqrt( x-4) ≥ 0
Squaring each side
x-4≥ 0
x≥ 4
The domain is [4,∞)
The bracket means it included the value, parentheses does not include the value)
The range is the value that output can take
The smallest value a square root can be is 0
y ≥ 0
The range is [0,∞)