input: Write a python function to convert a list of numbers to a dictionary where each key is the number and the value is its square root.
  assert to_dict([1, 4, 9]) == {1: 1.0, 4: 2.0, 9: 3.0}
  assert to_dict([16, 25, 36]) == {16: 4.0, 25: 5.0, 36: 6.0}
  assert to_dict([49, 64, 81]) == {49: 7.0, 64: 8.0, 81: 9.0}
output: import math
  
  def to_dict(numbers):
      return {num: math.sqrt(num) for num in numbers}