# Demand Function

In cost and demand problems, why is the equation for price per unit named the demand function, as shown in the examples below? Also, why is it equal to a constant minus some multiple of the number of units sold? The cost function's formula makes sense; the two terms represent fixed costs and the variable costs of each unit sold, but I seem don't seem to understand what the demand function is saying.

• If it confuses you then simply rearrange to equation so that it states total units in terms of a constant minus some price. Typically, one can just solve for equilibrium price and then determine the equilibrium production. Just do whatever makes most sense to you. – 123 Jul 9 '18 at 13:58
• In addition to @123 s answer economists are sometimes a bit sloppy with their terminology. What you're really looking at is an inverse demand function. In graphical analysis this is also typically what is drawn (for historic reasons) and called a demand curve. – Maarten Punt Jul 9 '18 at 17:21