input: Write a function to combine two strings and reverse the result in Python. The function should take two input strings 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("OpenAI ", "ChatGPT")=="TPGtahC IAnepO"
  assert reverse_combined_strings("", "example")=="elpmaxe"
output: def reverse_combined_strings(str1, str2):
      return (str1 + str2)[::-1]