input: Write a function to combine two strings and reverse the result in Python. The function should take two input strings and return the combined string reversed. If the input strings are empty, the function should return an empty string.
  assert reverse_combined_string("Hello ", "world!")=="!dlrow olleH"
  assert reverse_combined_string("abc", "def")=="fedcba"
  assert reverse_combined_string("", "test")=="tset"
  assert reverse_combined_string("example", "")=="elpmaxe"
  assert reverse_combined_string("", "")==""
output: def reverse_combined_string(s1, s2):
      return (s1 + s2)[::-1]