ECON2209 Lecture Notes - Lecture 5: January 30, Budget Constraint, Indifference Curve
January 30th
(1.) Consumer Theory Budget Constraint
● Marginal ability to trade (MAT)... slope
● Relative price of X in terms of Y
● Opportunity cost (marginal cost)
● Change in income:
○ Pushes the budget constraint outward or inward
● Changes in prices
○ One price:
■ Rotation of the budget constraint, the price that doesn't change is the
anchor that it pivots from
○ Both prices
■ 2 intercepts change
■ Slope MAY change
● Except when both prices change at same rate…. Parallel shift
● 2. Indifference Curve
○ What a consumer wants
○ Tastes in preferences as well as utility
○ Shows the combinations of 2 goods that provide same level of utility
● Most indifference curves are Y axis and X axis with concave
● They do not cross, as they are
○ Downward sloping
○ Higher Indifference curves are preferred
○ Convex
○ DO NOT CROSS
● Perfect substitutes are straight lines like a budget constraint
● Perfect compliments: right angle lines
● MRS:
○ Marginal Rate of Substitution
○ MRS = Slope of the indifference curve…. changey/changex
○ Should equal: -MUX/MUY
○ Say we are on the indifference curve….
■ U(x,Y) = U1
● Always U1 anywhere on this curve
■ Differentiate DU/DX*Dx+DU/DY*DY= 0
■ dy/dx = -MUX/MUY
○ Graphically
■ MRS at point A… slope of the graph at point A
■ Draw a tangent line….
■ The MRS at point A is the slope of the tangent line to the indifference
curve!
■ As we move down the curve, the MRS gets smaller and smaller
○ Interpretation of the slope (MRS)
■ 1. Marginal Willingness to Trade (MWT)
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Document Summary
Relative price of x in terms of y. Pushes the budget constraint outward or inward. Rotation of the budget constraint, the price that doesn"t change is the anchor that it pivots from. Except when both prices change at same rate . Tastes in preferences as well as utility. Shows the combinations of 2 goods that provide same level of utility. Most indifference curves are y axis and x axis with concave. They do not cross, as they are. Perfect substitutes are straight lines like a budget constraint. Mrs = slope of the indifference curve . changey/changex. Say we are on the indifference curve . Mrs at point a slope of the graph at point a. The mrs at point a is the slope of the tangent line to the indifference curve! As we move down the curve, the mrs gets smaller and smaller. The rate at which consumer is willing to trade x for y, without a change in utility.