input: Write a function to combine two given strings and then reverse the combined result in Python. The function should take two strings as input and return the reversed combined string.
  assert reverse_combined_strings("Hello ", "world!")=="!dlrow olleH"
  assert reverse_combined_strings("Python ", "Programming")=="gnimmargorP nohtyP"
  assert reverse_combined_strings("a", "b")=="ba"
output: def reverse_combined_strings(str1, str2):
      combined = str1 + str2
      return combined[::-1]