1. Loose Ends

2. Dead Weight Loss
Let Q* be the output that maximizes surplus plus profits. Let CS* and * be these profits.
Let Q be any other output. Let CS and  be the surplus and profits at this other Q.
DWL = CS* + * -(CS + )

3. Opportunity Cost
When one considers using an asset or input for a particular use,
The opportunity cost of an asset or input is its value in its best use other than the particular use being considered.
EX: I worked for my Dad. The opportunity cost is the value of my labor working for the highest paying employer other than my Dad.

4. Isoquants Again Axes are quantity of input.
Qth-Isoquant is all input bundles that produce the output Q.
-P2 / P1 is slope of isocost line
Draw (or look at ) isoquant
Draw any isocost line with slope -P2 / P1
Use drawn line as guide and visually construct parallel line that is tangent to isoquant

5. Isoquants Again and Again
Now mark the input bundle at tangency
Read off the amounts of inputs 1 and 2, x1 and x2.
Calculate P1 x1 + P2 x2. This is what it cost to make Q in a least cost fashion.