Answer:
g(x) = -√(x+6)
Step-by-step explanation:
The inverse of the function y = f(x) can be found by solving for y the relation x = f(y).
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x = f(y)
x = y^2 -6
x +6 = y^2 . . . . . . add 6
-√(x +6) = y . . . . . negative square root
The negative root produces y ≤ 0, equivalent to x ≤ 0 for f(x).
The inverse of f is g(x) = -√(x +6).
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Additional comment
The graph of a function and its inverse are mirror images of each other across the line y=x. This is shown in the attachment for the f(x) and g(x) in this problem.