Lecture 4: Mathematical Methods in Economics and Finance
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Questions and Answers

What is the condition for the limit to exist when defining the infinite sum?

  • 0 < |q| < 1 (correct)
  • q must be greater than 1
  • n must be less than N
  • n must approach negative infinity
  • For all values of |q| greater than 1, the limit of q^n does not go to zero as n approaches infinity.

    True (A)

    What does the continuity of a function on an interval imply regarding its graph?

    The graph can be drawn without lifting the pencil off the paper.

    The definitions of continuity are equivalent when the limits satisfy the criteria for ______.

    <p>epsilon-delta</p> Signup and view all the answers

    Match the term with its description regarding continuity:

    <p>Continuity at a point = The limit of f(x) as x approaches c equals f(c) Open interval = An interval that does not include its endpoints Graph continuity = Can be drawn without lifting pencil Discontinuity = A point where the function is not continuous</p> Signup and view all the answers

    Using the Binomial formula, which term indicates that q < 1?

    <p>n𝜒 (D)</p> Signup and view all the answers

    All functions studied previously are continuous.

    <p>False (B)</p> Signup and view all the answers

    What is the relationship between the value of q and the limit of q^n as n approaches infinity?

    <p>The limit approaches zero if 0 &lt; |q| &lt; 1.</p> Signup and view all the answers

    What is the second point chosen to find the tangent line for the function f(x) = x^3 near x = 2?

    <p>(3, 27) (C)</p> Signup and view all the answers

    The equation of a tangent line can be written using only one point on the function.

    <p>False (B)</p> Signup and view all the answers

    What is the value of f(2) for the function f(x) = x^3?

    <p>8</p> Signup and view all the answers

    The equation of the tangent line at x = 2 is given by ŷ = _____ · x̂ - 30.

    <p>19</p> Signup and view all the answers

    Match the following values to their corresponding points on the function f(x) = x^3:

    <p>(2, 8) = f(2) = 8 (3, 27) = f(3) = 27 (1.5, 3.375) = f(1.5) = 3.375 (x, f(x)) = General point on the function</p> Signup and view all the answers

    What is the purpose of finding a tangent line to the graph of a function?

    <p>To approximate the function near a point (A)</p> Signup and view all the answers

    The function f(x) = x^3 is continuous everywhere.

    <p>True (A)</p> Signup and view all the answers

    What is the slope of the tangent line calculated using the points (2, 8) and (3, 27)?

    <p>19</p> Signup and view all the answers

    What is the limit value as n approaches infinity of the expression $\frac{x_n^3 - 8}{x_n - 2}$ when $x_n$ approaches 2?

    <p>12 (A)</p> Signup and view all the answers

    The expression $\frac{x_n^3 - 8}{x_n - 2}$ directly equals $x_n^2 + 2x_n + 4$ at $x_n = 2$.

    <p>False (B)</p> Signup and view all the answers

    What does $k_n$ converge to as $x_n$ approaches 2 in the linear approximation example?

    <p>12</p> Signup and view all the answers

    The derivative is defined for a function $f: D \rightarrow \mathbb{R}$ if certain limits exist at points _____ and _____ within the domain.

    <p>a, b</p> Signup and view all the answers

    Match the following expressions to their corresponding components in the example.

    <p>$x_n^3 - 8$ = Numerator of the limit expression $x_n - 2$ = Denominator of the limit expression $k_n$ = Slope of the linear approximation $12$ = Limit value as $n \to \infty$</p> Signup and view all the answers

    Which of the following expressions represent the dependent relationship of $x_n$?

    <p>$x_n = 2 + (x_n - 2)$ (C)</p> Signup and view all the answers

    As $x_n$ approaches 2, the term $(x_n - 2)^2$ tends to zero.

    <p>True (A)</p> Signup and view all the answers

    What type of function does the expression $y = \frac{x_n^3 - 8}{x_n - 2}$ approximate?

    <p>A cubic function</p> Signup and view all the answers

    What must a function be if it is differentiable at a point?

    <p>Continuous at that point (C)</p> Signup and view all the answers

    The Squeeze Theorem is applied to prove that if a function is differentiable, it converges to zero.

    <p>True (A)</p> Signup and view all the answers

    What is the formula provided by the Product Rule for differentiation?

    <p>(f · g)'(x) = f'(x) · g(x) + f(x) · g'(x)</p> Signup and view all the answers

    If two functions f and g are differentiable at point x, their product (f · g) is also ______ at that point.

    <p>differentiable</p> Signup and view all the answers

    Match the terms with their definitions:

    <p>Differentiable = A function has a derivative at a point Continuous = A function does not have any jumps or breaks Squeeze Theorem = A method to find limits of functions Product Rule = A formula for differentiating products of functions</p> Signup and view all the answers

    Which statement about the continuity of differentiable functions is true?

    <p>A differentiable function is continuous. (B)</p> Signup and view all the answers

    For arbitrary sequence (x_n) such that x_n → x, we can say that ______ is an important aspect of differentiability.

    <p>continuity</p> Signup and view all the answers

    The limit lim |f'(x) · (x_n - x)| + |x_n - x| approaches zero as n approaches infinity.

    <p>True (A)</p> Signup and view all the answers

    What is the derivative of $x^2$?

    <p>$2x$ (A)</p> Signup and view all the answers

    The derivative of $ rac{1}{x}$ is $- rac{1}{x^2}$.

    <p>True (A)</p> Signup and view all the answers

    What is the general formula for deriving $x^{k+1}$?

    <p>$(k + 1)x^k$</p> Signup and view all the answers

    The derivative of $(x^3)'$ is _____.

    <p>3x^2</p> Signup and view all the answers

    Match the following derivatives with their functions:

    <p>$(x^2)'$ = $2x$ $( rac{1}{x})'$ = $- rac{1}{x^2}$ $(x^3)'$ = $3x^2$ $(x^k)'$ = $kx^{k-1}$</p> Signup and view all the answers

    Which theorem is used to calculate the derivative of a natural power of $x$?

    <p>Product rule (B)</p> Signup and view all the answers

    The function $f(x) = rac{1}{x}$ is not differentiable at $x = 0$.

    <p>True (A)</p> Signup and view all the answers

    What is the derivative of $x$, denoted as $(x)'$?

    <p>$1$</p> Signup and view all the answers

    What does the notation f ′ (x) represent?

    <p>The derivative of function f at point x (C)</p> Signup and view all the answers

    The derivative of a function exists if the limit does not depend on the choice of sequence xn.

    <p>False (B)</p> Signup and view all the answers

    What is required for a function to be differentiable at point x?

    <p>The limit defining the derivative must exist and be the same regardless of the sequence chosen.</p> Signup and view all the answers

    The derivative f ′ (x) is defined using the limit of the expression ___ as n approaches infinity.

    <p>(f(xn) - f(x)) / (xn - x)</p> Signup and view all the answers

    Which of the following statements about differentiability is true?

    <p>A function is differentiable at x if the derivative exists and is the same for all sequences. (C)</p> Signup and view all the answers

    A function must be defined on an interval (a, b) to have a derivative at point x.

    <p>True (A)</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>f ′ (x) = The derivative of function f at point x Differentiable = If the derivative exists at a point Limit = Value that function approaches as inputs approach a point Sequence = A list of numbers approaching a specific value</p> Signup and view all the answers

    For the derivative to exist at point x, the limit must approach the same ___ independently of the choice of sequence.

    <p>number</p> Signup and view all the answers

    Flashcards

    Infinite Geometric Series

    A mathematical concept representing an infinite sum, where each term is calculated by multiplying the previous term by a constant factor.

    Common Ratio (q) in a Geometric Series

    A constant value, used to multiply each term in a geometric series to obtain the next term.

    Convergence of an Infinite Geometric Series

    The sum of an infinite geometric series converges to a finite value if the absolute value of the common ratio (|q|) is less than 1. The value of the sum is given by the formula: (first term) / (1 - common ratio).

    Limit of a Sequence (lim n→∞)

    The limit of a sequence is the value that the sequence approaches as the number of terms increases infinitely.

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    Continuity of a Function

    A function is said to be continuous at a point 'x' if the function's value at 'x' and the value the function approaches as 'x' is approached from both sides are identical. Informally, this means the graph of the function can be drawn without lifting the pen.

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    Continuity on an Open Interval

    A function is continuous on an open interval if it is continuous at every point within that interval.

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    Tangent line

    A straight line that touches a curve at a single point and has the same slope as the curve at that point.

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    Linear approximation

    A method of approximating a function with a straight line near a given point.

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    Derivative of a function

    The slope of the tangent line to a function at a given point.

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    Secant line

    The line formed by connecting two points on a curve.

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    Limit definition of the derivative

    The process of finding the slope of the secant line as the two points get closer and closer together.

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    Function

    A way to express the relationship between two variables, where one variable changes in response to another.

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    Linear function

    A function that can be represented by a straight line.

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    Nonlinear function

    A function that can be represented by a curve.

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    Derivative

    A mathematical concept that describes the instantaneous rate of change of a function at a specific point. It is represented by the derivative of the function.

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    L'Hopital's Rule

    A technique used to find the limit of an expression where the variable approaches a specific value, and the expression itself takes on an indeterminate form (e.g., 0/0). This technique involves algebraic manipulation to eliminate the indeterminate form and evaluate the limit.

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    Derivative at a Point

    The value of the derivative of a function at a specific point. It represents the slope of the tangent line to the function's graph at that point.

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    Limit Definition of Derivative

    A technique for calculating the derivative of a function by expressing it in terms of a small increment (h), applying the function to the incremented value, and then taking the limit as h approaches zero.

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    Integration

    The process of finding the antiderivative of a function. It involves reversing the process of differentiation.

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    Instantaneous Rate of Change

    A mathematical expression that represents the instantaneous rate of change of a function with respect to its independent variable. It is found by finding the derivative of the function.

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    Differential Equation

    A function that describes the relationship between a variable and its rate of change. It is used to model physical phenomena that involve rates of change, such as population growth or radioactive decay.

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    Differentiable function

    A function f is differentiable at a point x if the limit of the difference quotient exists and is equal to the same number, regardless of the sequence used to approach x.

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    Neighborhood of x

    For a function f to have a derivative at a point x, the function must be defined within some small interval around x. In other words, the function must be defined in a 'neighborhood' of the point.

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    Local behavior of a function

    The derivative of a function at a point x is determined solely by the function's behavior in the immediate vicinity of that point. It's about the function's 'local' behavior, not its global behavior.

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    Independent of sequence

    The choice of the sequence used to approach x in the difference quotient does not affect the value of the derivative if it exists. This means the limit of the difference quotient is independent of the specific way we approach x.

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    Derivative of x^k

    The derivative of 'x' raised to a power 'k' (where 'k' is a positive integer) is equal to 'k' times 'x' raised to the power 'k-1'.

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    Derivative of 1/x

    The derivative of 1/x is equal to -1/x^2.

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    Differentiability of a function

    A function is differentiable at a point x if its derivative exists at that point, which means the function has a well-defined tangent line at that point.

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    Differentiability implies Continuity

    If a numerical function f is differentiable at point x, it must also be continuous at point x. This means that a function that has a derivative at a point must also be smooth and unbroken at that point.

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    Product Rule for Differentiation

    The product rule states that the derivative of the product of two differentiable functions f and g is equal to the sum of the product of the first function and the derivative of the second function, plus the product of the derivative of the first function and the second function.

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    Applying the Product Rule

    The product rule is used to find the derivative of a function that is the product of two other functions. It simplifies the process by breaking down the derivative into smaller, more manageable parts.

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    Importance of the Product Rule

    The product rule is a fundamental concept in calculus that helps to find derivatives of complex functions. Understanding it allows you to differentiate a wider range of functions, including those with products of functions as part of their structure.

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    Convergence of a sequence

    Any sequence (xn) that approaches a finite value x as n approaches infinity is said to converge to x. This means that the terms of the sequence get arbitrarily close to x as n becomes very large.

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    Study Notes

    Lecture 4: Mathematical Methods in Economics and Finance

    • Topic Outline:
      • Limits and infinite sums
      • Continuity of a function
      • Derivative of a function
      • Composition of functions (next lecture)

    Limits of Sequences

    • Definition: A number x is the limit of a sequence (an) if, for any ε > 0, there exists a natural number N such that for all n > N, |an - x| < ε. In this case, the sequence converges.
    • Infinite Limits: A sequence (an) tends to infinity if, for any M, there exists N ∈ N such that for all n > N, an > M. A sequence tends to minus infinity similarly, with an < M for all n > N.
    • Finite Limits Theorem: A sequence of real numbers has at most one finite limit. This generalizes to infinite limits as well.

    Arithmetic Properties of Limits

    • Theorem L3.2 (Sum): If sequences (an) and (bn) have finite limits, then (an + bn) also has a finite limit; moreover, lim (an + bn) = lim an + lim bn
    • Theorem L3.3 (Product): If sequences (an) and (bn) have finite limits, then (anbn) also has a finite limit; moreover, lim (anbn) = lim an • lim bn
    • Theorem L3.4 (Quotient): If sequences (an) and (bn) have finite limits, and lim bn ≠ 0, then (an/bn) also has a finite limit; moreover, lim (an/bn) = lim an / lim bn

    Infinite Sums

    • Definition: Given a sequence aj, the infinite sum Σj=1 aj is defined as the limit limn→∞ Σj=1n aj, if this limit exists.

    Infinite Sums - Example

    • Example 1: Consider Σj=0 qj, where 0 < |q| < 1. The sum is equal to 1/(1 - q), when |q| < 1.

    Squeeze Theorem for Sequences

    • Theorem L4.1 (Squeeze Theorem): If an ≤ bn ≤ cn for all n ∈ N, and lim an = lim cn = x, then lim bn = x.

    Continuity of Functions

    • Definition: A function f : D → R is continuous at a point x ∈ (a, b) if for any sequence (xn) of real numbers such that xn → x, there exists limn→∞ f(xn) and limn→∞ f(xn)=f(x).
    • Alternative Definition: A function f : D → R is continuous at x ∈ (a, b) if, for any ε > 0, there exists a δ > 0 such that |f(z) - f(x)| < ε for all z such that |z - x| < δ.

    Continuity of Functions (Geometric Interpretation)

    • Geometrically, continuity means the graph of the function can be drawn without lifting the pen.

    Derivatives

    • Definition: The derivative of a function f at a point x is defined as f'(x) = limxn→x (f(xn)-f(x))/(xn-x) , given that the limit exists.

    Derivative of a Linear Function

    • Definition: f(x) = ax + b is differentiable at any point x for all real values of x and f'(x) = a

    Derivative of xk

    • Theorem L4.3: The function f(x) = xk, where k ∈ N is differentiable and f'(x) = kxk-1.
    • Proof: Uses the Binomial Theorem to evaluate the limit.

    Additivity of the Derivative

    • Theorem L4.4: The sum of two differentiable functions is also differentiable, and its derivative is the sum of the derivatives of the two functions: (f+g)'(x) = f'(x) + g'(x)

    Differentiability Implies Continuity

    • Theorem L4.5: If a function is differentiable at a point, then it is continuous at that point.

    Product Rule for Differentiation

    • Theorem L4.6: The derivative of the product of two functions is given by (fg)'(x) = f'(x)g(x) + f(x)g'(x).

    Corollary (Constant Multiple Rule)

    • For any constant c ∈ R and differentiable function f, the derivative of c·f(x) is given by (cf)'(x) = c·f'(x)

    Additional Information (Examples)

    • Derivatives are shown for polynomial functions (x3 and higher orders) and for 1/x.
    • The slides cover composition of functions and related properties.

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    Description

    This quiz covers the key concepts discussed in Lecture 4 on Mathematical Methods in Economics and Finance. Topics included are limits and infinite sums, continuity, derivatives, and sequence limits. Understand the fundamental principles that apply to sequences and their limits within economic contexts.

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