The expression for k(x) is k(x) = x.
The function k(x) can be found by applying the inverse operation to the given function f(x) = -√x. Since the inverse operation of taking the square root is squaring, we can express k(x) as follows:
k(x) = (-√x)2
Simplifying further:
k(x) = (-1)2*(√x)2
k(x) = 1*x
Therefore, the expression for k(x) is k(x) = x.