Please help if u see this

Domain = [-3, infinity)

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Work Shown:

In step 2, we replaced every x with g(x)

In step 3, we plugged in g(x) = sqrt(x+3)

The domain of g(x) is [-3, infinity), so this is the domain of as well since the composite function depends entirely on g(x). Put another way: the input of f(x) depends on the output of g(x), so that's why the domains match up.