input: Write a function that converts a given temperature value from Fahrenheit to Celsius. The input is the temperature in Fahrenheit and the output is the temperature in Celsius, rounded to two decimal places. If the input temperature is None, return None.
  assert fahrenheit_to_celsius(32)==0.0
  assert fahrenheit_to_celsius(212)==100.0
  assert fahrenheit_to_celsius(-40)==-40.0
  assert fahrenheit_to_celsius(98.6)==37.0
  assert fahrenheit_to_celsius(None)==None
output: def fahrenheit_to_celsius(fahrenheit):
      if fahrenheit is None:
          return None
      return round((fahrenheit - 32) * 5 / 9, 2)