EC311

List the feasible set first, then compare every stationary point and boundary.

Utility ranks bundles, while MRS measures the local trade-off the consumer accepts.

At an interior choice, willingness to trade equals the market trade-off.

Preference shape determines the solution rule, so tangency cannot be imposed everywhere.

A variable on an axis creates movement along a curve; an off-axis variable shifts it.

Price the old bundle at new prices to isolate substitution before restoring actual purchasing power.

Find the least-cost budget at new prices tangent to the original indifference curve.

Giffen behavior requires an opposing income effect large enough to overturn substitution.

Cash expands choice without a composition rule; taxes and in-kind aid reshape the budget differently.

Matching makes one donor baht create more than one recipient baht, rotating the giving constraint.

The wage is both the price of leisure and hourly income, creating opposing substitution and income effects.

Choosing A when B was affordable reveals that A is at least as good as B.

The base basket ignores substitution and tends high; the current basket tends low.

The intertemporal budget combines income in present value, and interest sets the c1–c2 slope.

Choose investment by NPV first, then use capital markets to time consumption.

Average utility across states because curvature captures risk attitudes.

Portfolio risk depends on each variance and their covariance, not merely asset count.

The risky share rises with excess return, falls with risk aversion and variance, and is clipped to feasible bounds.

Marginal product changes one input; returns to scale scales all inputs.

At an interior optimum, marginal product per baht is equalized, so MRTS equals relative input prices.

A marginal value below an average pulls it down and one above pushes it up, so they meet at the minimum.

Scale changes current output, scope changes joint production, and learning changes cost with accumulated experience.

Produce where P=MC if price covers AVC; fixed cost does not alter the short-run shutdown rule.

Entry expands industry supply until economic profit is zero at P=min LAC in a constant-cost industry.

A tax creates Pc−Ps=t, reduces trade, and burdens the less elastic side more.

World price opens trade; restrictions raise domestic price, transfer surplus, and destroy some gains from trade.

Choose Q from MR=MC, read P from demand, and allocate across plants by equalizing MC.

Allocate so each market’s MR equals common MC, then price from that market’s demand.

Each instrument extracts surplus or allocates shared capacity differently, so match the model to the constraint.

Entry shifts each firm’s demand until it is tangent to ATC, while downward slope preserves markup.

Cournot intersects simultaneous best responses; Stackelberg substitutes the follower response into the leader’s profit.

Bertrand tests undercutting, a leader faces residual demand, and a cartel allocates joint output like multiple plants.

Nash is a strategy profile where no player gains from a unilateral deviation.

Sequential games use backward induction; repeated games compare today’s deviation gain with future punishment.

When a rival raises price, our demand improves, often making a higher own price optimal under strategic complements.

Hire until marginal revenue product equals factor price; rent is payment above the minimum needed to retain supply.

A buyer facing upward factor supply has ME above wage, so it sets ME=MRPL and reads wage from supply.

Conditional demand holds output fixed for substitution; unconditional demand lets profit-maximizing output change.

Prices change both endowment wealth and choices, so everyone must optimize and all markets clear together.

Efficiency requires equal MRTS and MRS=MRT, while welfare criteria still choose distribution.

Add marginal external cost or benefit to the private side and find the social intersection.

Everyone consumes the same public-good quantity, so willingness to pay adds; common resources are rival but hard to exclude.

Hidden type precedes contracting and calls for screening or signaling; hidden action follows contracting and calls for incentives or monitoring.