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Answer:
 (b) x ≥ 1; f⁻¹(x) = 1+√(x+1)
Explanation:
We can find the inverse function by solving for y:
 x = f(y)
 x = y² -2y
 x +1 = y² -2y +1
 x +1 = (y -1)²
 √(x +1) = y -1
 1 +√(x +1) = y
So, the inverse function is ...
 

For this, the root will be non-negative, so the minimum value of this function is 1. That is, the minimum value of x for which the original function has this as an inverse is 1.
The domain restriction is x ≥ 1.
The inverse function is f⁻¹(x) = 1+√(x+1)