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Fundamental theorem of calculus and definite integrals

Fundamental theorem of calculus and definite integrals

The Fundamental Theorem of Calculus links the concepts of differentiation and integration, providing a comprehensive framework for understanding their relationship.

  1. First Part: It states that if ff is a continuous function on the interval [a,b][a, b], and FF is an antiderivative of ff (meaning F=fF' = f), then

    abf(x)dx=F(b)F(a).\int_a^b f(x) \, dx = F(b) - F(a).

    This part essentially tells us that the definite integral of a function can be computed using its antiderivative.

  2. Second Part: It asserts that if ff is a continuous function on [a,b][a, b], then the function defined by

    F(x)=axf(t)dtF(x) = \int_a^x f(t) \, dt

    is continuous on [a,b][a, b] and differentiable on (a,b)(a, b), with its derivative given by F(x)=f(x)F'(x) = f(x).

Together, these two parts establish that integration can be seen as a way to accumulate values (areas under curves), while differentiation measures how these values change, thereby forming a fundamental connection in calculus.

Part 1: The fundamental theorem of calculus and definite integrals

There are really two versions of the fundamental theorem of calculus, and we go through the connection here.

Here are the key points to focus on when studying the Fundamental Theorem of Calculus (FTC) and definite integrals:

  1. Definition of Derivative and Integral:

    • Understand the relationship between differentiation and integration.
    • The derivative measures the rate of change, while the integral represents the accumulation of quantities.
  2. Fundamental Theorem of Calculus:

    • Part 1: If ff is continuous on [a,b][a, b] and FF is an antiderivative of ff on that interval, then:
      abf(x)dx=F(b)F(a)\int_a^b f(x) \,dx = F(b) - F(a)
    • Part 2: If ff is continuous on [a,b][a, b], then the function FF, defined by:
      F(x)=axf(t)dtF(x) = \int_a^x f(t) \,dt
      is continuous on [a,b][a, b], differentiable on (a,b)(a, b), and F(x)=f(x)F'(x) = f(x).
  3. Definite Integrals:

    • The definite integral calculates the net area under the curve of a function over an interval [a,b][a, b].
    • Properties of definite integrals include:
      • Linearity: ab[cf(x)+g(x)]dx=cabf(x)dx+abg(x)dx\int_a^b [cf(x) + g(x)]\,dx = c\int_a^b f(x)\,dx + \int_a^b g(x)\,dx
      • Additivity: abf(x)dx+bcf(x)dx=acf(x)dx\int_a^b f(x)\,dx + \int_b^c f(x)\,dx = \int_a^c f(x)\,dx
      • Reversal of limits: abf(x)dx=baf(x)dx\int_a^b f(x)\,dx = -\int_b^a f(x)\,dx
  4. Applications:

    • Use definite integrals to solve problems related to area, volume, work, and other physical applications.
    • Understand how to apply the FTC to evaluate definite integrals efficiently.
  5. Limit of Riemann Sums:

    • Recognize that the definite integral can be defined as the limit of Riemann sums as the partition of the interval becomes infinitely small.
  6. Techniques of Integration:

    • Familiarize yourself with methods such as substitution, integration by parts, and recognizing standard forms, as they will assist in finding antiderivatives F(x)F(x).

By mastering these key points, you'll gain a solid foundation in understanding the Fundamental Theorem of Calculus and the concept of definite integrals.

Part 2: Antiderivatives and indefinite integrals

What's the opposite of a derivative?  It's something called the "indefinite integral".

Here are the key points to learn when studying "Antiderivatives and Indefinite Integrals":

  1. Definition: An antiderivative of a function f(x)f(x) is a function F(x)F(x) such that F(x)=f(x)F'(x) = f(x). The indefinite integral symbol f(x)dx\int f(x) \, dx represents the family of all antiderivatives of f(x)f(x).

  2. Notation: The notation for the indefinite integral is f(x)dx=F(x)+C\int f(x) \, dx = F(x) + C, where CC is the constant of integration, accounting for all possible vertical shifts in the antiderivative.

  3. Basic Antiderivative Rules:

    • Power Rule: xndx=xn+1n+1+C\int x^n \, dx = \frac{x^{n+1}}{n+1} + C for n1n \neq -1.
    • Constant Multiple Rule: kf(x)dx=kf(x)dx\int k f(x) \, dx = k \int f(x) \, dx, where kk is a constant.
    • Sum/Difference Rule: (f(x)+g(x))dx=f(x)dx+g(x)dx\int (f(x) + g(x)) \, dx = \int f(x) \, dx + \int g(x) \, dx.
  4. Common Antiderivatives:

    • exdx=ex+C\int e^x \, dx = e^x + C
    • sin(x)dx=cos(x)+C\int \sin(x) \, dx = -\cos(x) + C
    • cos(x)dx=sin(x)+C\int \cos(x) \, dx = \sin(x) + C
    • sec2(x)dx=tan(x)+C\int \sec^2(x) \, dx = \tan(x) + C
  5. Techniques of Integration:

    • Substitution: Used when integrands are compositions of functions.
    • Integration by Parts: Based on the product rule, useful for products of functions.
    • Partial Fraction Decomposition: Useful for rational functions.
  6. Fundamental Theorem of Calculus: Establishes the connection between differentiation and integration. It asserts that if F(x)F(x) is an antiderivative of f(x)f(x) on an interval [a, b], then:

    abf(x)dx=F(b)F(a)\int_a^b f(x) \, dx = F(b) - F(a)
  7. Applications: Antiderivatives are used for calculating areas under curves, solving differential equations, and in physics for determining quantities like displacement from velocity.

  8. Practice: Regular practice is essential for mastering antiderivatives, including solving a variety of problems and using different techniques of integration.

Understanding these key points will provide a solid foundation for further study and application of antiderivatives and indefinite integrals in calculus.