input: Write a python function to sort a list of integers in descending order using the sorted function with a lambda function as the key parameter.
  assert sort_descending([8, 0, 7, 4, 5, 6, 9])==[9, 8, 7, 6, 5, 4, 0]
  assert sort_descending([1, 3, 2, 8, 5, 7])==[8, 7, 5, 3, 2, 1]
  assert sort_descending([10, 20, 5, 15])==[20, 15, 10, 5]
output: def sort_descending(lst):
      return sorted(lst, key=lambda x: -x)