Basically we write down the functions are invertible. And we use them both ways, it's the bottom line. It doesn't we're really writing down equilibrium in Q and P. It doesn't really matter what X and Y is. We're really just writing down an equilibrium relationship. It's just the convention is to put Q on the X- axis. Even though the convention will sometimes write demand curves with P on the left hand side the graphic convention will never change but How I write the curves might change How I write the equations might change You use opportunity cost to justify why demand sloping? Great question. Okay, let's go through it. That's exactly the kind of question I want to hear this semester. Is does someone want to take a crack at it? Anyone want to explain? and speak up If the price is higher to in order to get that rose, you had to give up more because the price represents sort of like your opportunity. Right, for the opportunity cost of any good in the...