input: Write a python function to find the square root of a number using recursion.
  assert abs(recursive_sqrt(64) - 8.0) < 0.0000009
  assert abs(recursive_sqrt(100) - 10.0) < 0.0000009
  assert abs(recursive_sqrt(49) - 7.0) < 0.0000009
output: def recursive_sqrt(n, guess=1.0):
      if abs(guess * guess - n) < 0.0000009:
          return guess
      else:
          new_guess = (guess + n / guess) / 2
          return recursive_sqrt(n, new_guess)