Definite Integral Properties

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Questions and Answers

If $f(x)$ is integrable and $a ≤ c ≤ b$, which property allows you to split the integral $\int_{a}^{b} f(x) dx$ into $\int_{a}^{c} f(x) dx + \int_{c}^{b} f(x) dx$?

  • Constant Multiple
  • Sum and Difference
  • Reversing Limits of Integration
  • Interval Additivity (correct)

Reversing the limits of integration in a definite integral does not affect the sign of the integral.

False (B)

What is the value of the definite integral $\int_{a}^{a} f(x) dx$?

0

The integral of a constant multiple of a function, $\int_{a}^{b} k \cdot f(x) dx$, is equal to k multiplied by the integral of the function, which is written as k $\cdot$ $\int_{a}^{b}$ ______ dx.

<p>f(x)</p>
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Match the following integral properties with their descriptions:

<p>$\int_{a}^{b} f(x) dx = -\int_{b}^{a} f(x) dx$ = Reversing Limits of Integration $\int_{a}^{b} k \cdot f(x) dx = k \cdot \int_{a}^{b} f(x) dx$ = Constant Multiple $\int_{a}^{b} [f(x) + g(x)] dx = \int_{a}^{b} f(x) dx + \int_{a}^{b} g(x) dx$ = Sum of Functions If $f(x) \ge 0$, then $\int_{a}^{b} f(x) dx \ge 0$ = Non-negative Function</p>
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If $f(x)$ is an odd function, what is the value of $\int_{-a}^{a} f(x) dx$?

<p>0 (C)</p>
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If $f(x) \ge g(x)$ for $a ≤ x ≤ b$, then $\int_{a}^{b} f(x) dx$ must be less than or equal to $\int_{a}^{b} g(x) dx$.

<p>False (B)</p>
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According to the comparison property, if $m ≤ f(x) ≤ M$ for $a ≤ x ≤ b$, what inequality can be stated about $\int_{a}^{b} f(x) dx$?

<p>$m(b - a) ≤ \int_{a}^{b} f(x) dx ≤ M(b - a)$</p>
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The absolute value of the definite integral is always ______ than or equal to the definite integral of the absolute value of the function.

<p>less</p>
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Which property is most useful for simplifying the integral of a piecewise defined function?

<p>Interval Additivity (D)</p>
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The integral of an even function $f(x)$ from $-a$ to $a$ is equal to zero.

<p>False (B)</p>
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What does the property $\int_{a}^{b} [f(x) ± g(x)] dx = \int_{a}^{b} f(x) dx ± \int_{a}^{b} g(x) dx$ allow you to do with the integral of a sum or difference of functions?

<p>Break it into simpler terms</p>
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Which of the following properties is most helpful when estimating bounds on an integral without explicitly solving it?

<p>Comparison Properties (B)</p>
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If $f(x)$ is _____, then $\int{-a}^{a} f(x) dx = 0$.

<p>odd</p>
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The absolute value property states that $\int_{a}^{b} f(x) dx \le |\int_{a}^{b} |f(x)| dx|$.

<p>False (B)</p>
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How does the integral $\int_{1}^{5} 3f(x) dx$ relate to $\int_{1}^{5} f(x) dx$?

<p>It is three times the value. (A)</p>
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Explain briefly why $\int_{-5}^{5} x^3 dx = 0$.

<p>$x^3$ is an odd function</p>
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$\int_{3}^{7} f(x) dx + \int_{7}^{9} f(x) dx = \int_{3}$ ______ $f(x) dx$.

<p>9</p>
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The absolute value of an integral can be greater than the integral of the absolute value of the function

<p>False (B)</p>
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If you know that $2 ≤ f(x) ≤ 4$ for $1 ≤ x ≤ 6$, what can you say about the value of $\int_{1}^{6} f(x) dx$?

<p>It must be between 4 and 24. (D)</p>
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Flashcards

Interval Additivity

The integral over an interval can be split into integrals over subintervals. ∫ab f(x) dx = ∫ac f(x) dx + ∫cb f(x) dx, for a ≤ c ≤ b.

Constant Multiple

A constant factor within an integral can be factored out: ∫ab k * f(x) dx = k * ∫ab f(x) dx.

Sum and Difference Rule

The integral of a sum/difference is the sum/difference of individual integrals: ∫ab [f(x) ± g(x)] dx = ∫ab f(x) dx ± ∫ab g(x) dx.

Reversing Limits

Switching the limits of integration changes the sign: ∫ba f(x) dx = -∫ab f(x) dx.

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Integral of Zero

The definite integral over an interval of zero length is zero: ∫aa f(x) dx = 0.

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Symmetric Functions

For even functions, ∫-aa f(x) dx = 2 * ∫0a f(x) dx. For odd functions, ∫-aa f(x) dx = 0.

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Comparison Properties

If f(x) ≥ g(x), then ∫ab f(x) dx ≥ ∫ab g(x) dx. If m ≤ f(x) ≤ M, then m(b - a) ≤ ∫ab f(x) dx ≤ M(b - a).

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Absolute Value Property

The absolute value of an integral is less than or equal to the integral of the absolute value: |∫ab f(x) dx| ≤ ∫ab |f(x)| dx.

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Study Notes

  • Definite integrals possess properties that facilitate their evaluation and manipulation.
  • These properties are fundamental in calculus and are used to simplify complex integrals.

Interval Additivity

  • If a function f(x) is integrable on an interval containing a point c, the integral over the entire interval can be split into integrals over subintervals.
  • For a ≤ c ≤ b: ∫ab f(x) dx = ∫ac f(x) dx + ∫cb f(x) dx.
  • Useful for piecewise defined functions, where the function's definition changes at certain points within the interval.
  • It allows breaking the integral into parts where the function has a consistent definition.
  • Also applicable when there's a discontinuity within the interval; can integrate up to the discontinuity and then start again on the other side.

Constant Multiple

  • A constant factor within the integrand can be factored out of the integral.
  • For any constant k: ∫ab k * f(x) dx = k * ∫ab f(x) dx.
  • Simplifies integrand by dealing with constant multipliers separately.
  • Useful when the integrand contains a constant that complicates the integration process.

Sum and Difference

  • The integral of a sum or difference of functions is the sum or difference of their individual integrals.
  • ∫ab [f(x) ± g(x)] dx = ∫ab f(x) dx ± ∫ab g(x) dx.
  • Facilitates integrating complex expressions by breaking them into simpler terms.
  • Applicable when the integrand is a combination of multiple terms that are easier to integrate separately.

Reversing Limits of Integration

  • Reversing the limits of integration changes the sign of the integral.
  • ∫ba f(x) dx = -∫ab f(x) dx.
  • Useful when the limits are in an order that is not conducive to direct integration.
  • Can be applied to satisfy certain conditions or to simplify the form of an expression.

Integral of Zero

  • The definite integral of a function over an interval of zero length is zero.
  • ∫aa f(x) dx = 0.
  • If the upper and lower limits of integration are the same, no area is accumulated.
  • A direct consequence of the definition of the definite integral.

Integrals of Symmetric Functions

  • Symmetric functions (even or odd) have properties that simplify definite integrals over symmetric intervals (e.g., [-a, a]).
  • If f(x) is even (f(-x) = f(x)), then ∫-aa f(x) dx = 2 * ∫0a f(x) dx.
  • If f(x) is odd (f(-x) = -f(x)), then ∫-aa f(x) dx = 0.
  • Exploits symmetry to reduce the computation needed.
  • Even functions: the area from -a to 0 is the same as the area from 0 to a.
  • Odd functions: the area from -a to 0 is the negative of the area from 0 to a, so they cancel out.

Comparison Properties

  • Comparison properties allow us to compare the values of definite integrals based on the integrands.
  • If f(x) ≥ 0 for a ≤ x ≤ b, then ∫ab f(x) dx ≥ 0.
  • If f(x) ≥ g(x) for a ≤ x ≤ b, then ∫ab f(x) dx ≥ ∫ab g(x) dx.
  • If m ≤ f(x) ≤ M for a ≤ x ≤ b, then m(b - a) ≤ ∫ab f(x) dx ≤ M(b - a).
  • Useful for estimating bounds on integrals.
  • The integral of a non-negative function is non-negative; area under the curve is above the x-axis.
  • If one function is greater than another, its integral over the same interval is also greater.
  • An integral can be bounded by the product of the interval length and the minimum/maximum value of the function on that interval.

Absolute Value Property

  • The absolute value of a definite integral is less than or equal to the definite integral of the absolute value of the function.
  • |∫ab f(x) dx| ≤ ∫ab |f(x)| dx.
  • Useful when dealing with functions that change sign within the interval of integration.
  • Provides an upper bound on the magnitude of the integral.
  • The integral of the absolute value represents the total area without regard to sign, which is always greater than or equal to the magnitude of the signed area.

Applying Properties

  • Use properties strategically to simplify integrals before attempting to evaluate them directly.
  • Look for opportunities to break integrals into smaller intervals, factor out constants, or exploit symmetry.
  • Comparison properties are handy when exact evaluation is difficult or unnecessary, and only bounds are required.
  • When facing complex integrals, consider each property to see if it can simplify the process.
  • Understanding properties can lead to more efficient and accurate solutions.

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