input: Write a function to convert a given temperature value from Fahrenheit to Celsius. If the given temperature is below absolute zero (Fahrenheit), print an error message and return None. Otherwise, return the temperature in Celsius rounded to two decimal places.
  assert fahrenheit_to_celsius(32)==0
  assert fahrenheit_to_celsius(212)==100
  assert fahrenheit_to_celsius(-40)==-40
  assert fahrenheit_to_celsius(-500)==None
output: def fahrenheit_to_celsius(fahrenheit):
      if fahrenheit < -459.67:
          print("Error: Temperature below absolute zero.")
          return None
      celsius = (fahrenheit - 32) * 5 / 9
      return round(celsius, 2)