Question and solution:
Suppose that the supply and demand curves can be described by the following two equations:
Q=3P-6
and
Q=120-3P
a. Which equation is the supply curve and which equation is the demand curve? How do you know?
Demand curve is Q=120-3P (because P increases, Q decreases)
Supply curve is Q=3P-6 (because P increases, Q increases).
My question is: how can I figure out witch equation should I choose that has decreasing or increasing in Q so I can know where to put it with demand curve or supply curve.