1. The problem statement, all variables and given/known data This actually part of the Friedman equation but it's the math part I'm having trouble with. I'm simplifying down to the nitty-gritty. a'/a = x a' = ax a = e^x And the lecturer said that when a rate of change is proportional to thing itself then you multiply the thing itself by exp. I don't recall learning about that rule. What is it's name so that I can go back and practice it.