input: 
  def calculate_thermal_impedance(temperatures: List[float], wavelengths: List[float], slopes: List[float]) -> float:
      """ Calculate the thermal impedance based on given temperatures, wavelengths, and slopes.
      The thermal impedance is calculated using the formula:
      R_th = dλ/dT / dλ/dD
      where dλ/dT is the change in wavelength per unit temperature, and dλ/dD is the change in wavelength per unit dissipated power.
      The thermal impedance is then returned as a float.
  
      >>> calculate_thermal_impedance([15.0, 20.0, 25.0], [1200.0, 1250.0, 1300.0], [2.0, 2.5, 3.0])
      10.0
      >>> calculate_thermal_impedance([20.0, 22.5, 25.0], [1300.0, 1320.0, 1340.0], [1.5, 1.7, 1.9])
      5.0
      """
  
output:     dT = temperatures[-1] - temperatures[0]
      dλ = wavelengths[-1] - wavelengths[0]
      dλ_dT = dλ / dT
      
      dD = sum(slopes)
      dλ_dD = dλ / dD
      
      R_th = dλ_dT / dλ_dD
      return R_th