Microeconomics,, 16th Canadian Edition

Rewrite this as

As long as the supply curve slopes upward, ;
therefore,.
28. In the text, we define MPC as an incremental ratio. For
mathematical treatment, it is sometimes convenient to define all
marginal concepts as derivatives: ,
, and so on.
29. The basic relationship is

Dividing through by yields

and thus

Next, take the first difference of the basic relationship to get

d(w⋅L =w+Ls⋅

s)

dLs

dw

dLs

MC=AC+Ls⋅ddLws

dw/dLs> 0

MC>AC

MPC=dC/dYD

MPS=dS/dYD

YD=C+S

YD

YYD = +

D

C

YD

S

YD

1 =APC+APS