Newton's Law of Cooling (not the formal definition): (change in time) = -ln ((Tf - S)/(Ti - S)) / k Tf = final temperature Ti = initial temperature S = temperature of environment k = heat transfer coefficient Say that you wanted to cool something (such as a person) to a negative temperature (Tf would be negative) and the temperature of the environment was positive. This would mean that you would have to take the -ln (-#). Obviously, you can't do this. In another situation, say the surrounding temperature was the same as the final temperature. This would mean that you would have to take the -ln (0) which can't be done. How can I apply this formula to these situations?