Here is a general way to decompose a function into the composition of more than one function.
First, make an ordered list of the operations performed on the input value by the function. (That is, imagine the steps you would do to evaluate the function for a given input). In this example, the operations are
(1) take the square root;
(2) multiply by -1; and
(3) raise e to that power
Since there are three operations, you could write the given function as the composition of three separate non-trivial functions.
To write the given function as the composition of two functions, combine two of the three steps into one. There are clearly two different ways you could do this:
(a) combine steps (1) and (2):
(1) take the square root and multiply by -1; and
(2) raise e to that power
The resulting decomposition is
OR...
(b) combine steps (2) and (3):
(1) take the square root; and
(2) multiply by -1 and raise e to that power
