input: Write a function to combine two given strings and reverse the resulting string. The function should take two input strings as parameters, concatenate them, reverse the concatenated result, and return the final reversed string.
  assert reverse_combined_strings("Hello ", "world!")=="!dlrow olleH"
  assert reverse_combined_strings("Good ", "morning!")=="!gninrom dooG"
  assert reverse_combined_strings("Python ", "Programming")=="gnimmargorP nohtyP"
  assert reverse_combined_strings("", "Test")=="tseT"
  assert reverse_combined_strings(" ", "result")=="tser "
output: def reverse_combined_strings(str1, str2):
      return (str1 + str2)[::-1]