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Readings for those who have problems with calculus. Mathematics for economists: Sydsæter , K., P. Hammond, 2008, "Essential Mathematics for Economic Analysis", 3rd ed., Prentice Hall. Fundamental Methods of Mathematical Economics, Kevin Wainwright, Alpha Chiang.
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Readings for those who have problems with calculus. Mathematics for economists: Sydsæter, K., P. Hammond, 2008, "Essential Mathematics for Economic Analysis", 3rd ed., Prentice Hall. Fundamental Methods of Mathematical Economics, Kevin Wainwright, Alpha Chiang. Mathematics for Economists, Carl P. Simon, Lawrence E. Blume
Derivatives - introduction • Suppose a car is accelerating from 30mph to 50mph. • At some point it hits the speed of 40mph, but when? • Speed = (distance travelled)/(time passed) • How is it possible to define the speed at a single point of time?
Approximations • Idea: find distance/time for smaller and smaller time intervals. • Here f shows how the distance is changing with the time, x. • The time difference is h while the distance travelled is f(x+h) – f(x).
The derivative • Our approximation of the speed is • As h gets smaller, the approximation of the speed gets better. • When h is infinitesimally small, the calculation of the speed is exact. • Leibniz used the notation dy/dx for the exact speed.
Example • f(x) = x2 • f(x+h) – f(x) = (x + h)2 – x2 = (x2 + 2xh + h2)- x2 = 2xh + h2 • Speed = (2xh + h2)/h = 2x + h • When h is infinitesimally small, this is just 2x.
Rules for Differentiation The derivative of a constant is zero. If the derivative of a function is its slope, then for a constant function, the derivative must be zero. example:
Rules for Differentiation We saw that if , . power rule This is part of a pattern. examples:
Rules for Differentiation Proof:
Rules for Differentiation constant multiple rule: examples:
Rules for Differentiation constant multiple rule: sum and difference rules: (Each term is treated separately)
Rules for Differentiation product rule: Notice that this is not just the product of two derivatives. This is sometimes memorized as:
Rules for Differentiation quotient rule: or
Formulas you should learn (Cxa)’=Cax(a-1); C, a – a real number (ex)’=ex (ax)’=axlna; a>0
Derivatives rules - summary , , , , c is a constant , for
Chain Rule Consider a simple composite function:
Chain Rule If is the composite of and , then: Find: example: Chain Rule:
Differentiation of Multivariate Functions • The partial derivative of a multivariate function f(x,y) with respect to x is defined as
Differentiation of Multivariate Functions f(x1,x2)= Cx1ax2b