Hello from MrBillDoesMath!
Answer:
+\- sqrt(x-2)
Discussion:
Let y = x^2 + 2 and let's solve for "x".
Replace x by y and y by x in the above equation:
x = y^2 + 2 subtract 2 from both sides
x -2 = y^2 take the square root of both sides
+\- sqrt(x-2) = y
and y is the desired inverse.
Thank you,
MrB