What is the inverse and domain of f(x)=x^2+4

The domain of the inverse of a function is the range of the original function

so find the range of f(x)
this is lowest to highest
we got the vertex is at (0,4)
and it goes to infinity
so range is from 4 to infinity

inverse
replace f(x) with y
switch x and y
solve for y
replace y with finverse

f(x)=x^2+4
y=x^2+4
x=y^2+4
x-4=y^2
y=√(x-4)
f⁻¹(x)=√(x-4)

inverse is f⁻¹(x)=√(x-4)
the domain is x≥4

To find the inverse let
y = x^2 + 4
x^2 = y - 4
x = sqrt(y - 4)

inverse f-1(x) = sqrt( x - 4)   

the domain of x^2 + 4  is   all real x

the domain of f-1(x) is  x>= 4