Intermediate Microeconomics · free preview

The Lagrange Method

The Lagrange method turns the tangency condition into mechanical algebra, append the budget with a multiplier, solve the first-order conditions, and read off demands together with the marginal value of income itself.

1. The recipe

The recipe

2. A weighted Cobb-Douglas worked out

A weighted Cobb-Douglas worked out

3. The general Cobb-Douglas demands

The general Cobb-Douglas demands

4. Reading lambda as the value of money

Reading lambda as the value of money

5. What the multiplier measures

At a Lagrange optimum, what does the multiplier lambda equal and mean?

6. The worked example's budget step

In the example u equal to x1 x2 squared, m 90, prices 3 and 1, tangency gives x2 equals 6 x1. What does the budget then produce?

7. The share law

For Cobb-Douglas utility with weights a and b, what fraction of income goes to good one?

8. Cross-price independence

What does the Cobb-Douglas demand x1 equals a over a plus b times m over p1 say about the effect of p2 on good one?

9. Demands for a weighted family

For u equal to x1 x2 squared with income 90 and prices 3 and 1, compute x1 at the optimum, and write the number.

10. The other good's quantity

Same consumer, compute x2 at the optimum, and write the number.

11. Utility at the weighted optimum

For u of x1 times x2 squared with income 90 and prices 3 and 1, the optimum is (10, 60). What utility does it deliver?

12. The share law in dollars

Under the same weighted utility, how many dollars flow to each good at the optimum?

13. Lambda from both margins

At the optimum (10, 60), lambda computed from either first-order condition gives what value?

14. A price doubles

For Cobb-Douglas demands, if p1 doubles while income and p2 hold, what happens to x1 star?

15. The multiplier at the optimum

For u of x1 times x2 squared with income 90 and prices 3 and 1, compute lambda at the optimum, and write the number.

16. The squared good after a price rise

Same consumer, if the price of good two rises to 2, compute the new optimal x2 from the share law, and write the number.

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