Name: riemann sum area estimates
Uploaded: 2026-01-12T12:24:45.000Z
Duration: 1 min 24 s
Channel: JoVE

L’intégration approximative est utilisée lorsque la valeur exacte d’une intégrale définie ne peut pas être calculée.Cela se produit généralement dans deux cas principaux : lorsque l’antidérivée de la fonction est inconnue ou n’existe pas sous une forme fermée, et lorsque la fonction est composée de données empiriques, telles qu’un ensemble de points discrets d’une expérience, plutôt qu’une formule continue.Dans de telles situations, les intégrales définies sont estimées à l’aide de sommes de Riemann, qui divisent l’intervalle en n sous-intervalles égaux de largeur Δx.Pour chaque sous-intervalle, un rectangle est construit, dont la hauteur est fixée par la valeur de la fonction à un point spécifique de ce sous-intervalle.Dans l’approximation de l’extrémité gauche Ln, la hauteur de chaque rectangle est fixée par la valeur de la fonction à l’extrémité gauche.Si la fonction augmente, cette méthode sous-estime la surface ; si la fonction diminue, elle surestime.L’approximation de l’extrémité droite Rn utilise l’extrémité droite de chaque sous-intervalle. Cette méthode surestime la surface si la fonction augmente, et inversement.Ces méthodes utilisent la géométrie de base — l’ajout de surfaces rectangulaires — pour estimer les intégrales de fonctions complexes ou inconnues.

intégration approximative

Dans de nombreux contextes pratiques et th&#xE9;oriques, la valeur exacte d&#x2019;une int&#xE9;grale d&#xE9;finie peut &#xEA;tre inaccessible. Cette limitation survient g&#xE9;n&#xE9;ralement lorsque la primitive d&#x2019;une fonction est inconnue ou ne peut &#xEA;tre exprim&#xE9;e sous une forme math&#xE9;matique explicite. Elle peut &#xE9;galement se produire lorsqu&#x2019;une fonction est d&#xE9;finie non par une formule, mais par un ensemble fini de points empiriques, tels que ceux recueillis lors d&#x2019;exp&#xE9;riences. Dans ces cas, les techniques d&#x2019;int&#xE9;gration approximative constituent une solution pr&#xE9;cieuse.
L&#x2019;une des approches les plus couramment utilis&#xE9;es consiste &#xE0; utiliser les sommes de Riemann, qui estiment l&#x2019;aire sous une courbe en subdivisant l&#x2019;intervalle d&#x2019;int&#xE9;gration en plusieurs parties &#xE9;gales. Chaque sous-intervalle est associ&#xE9; &#xE0; un rectangle dont la hauteur est d&#xE9;termin&#xE9;e par la valeur de la fonction en un point choisi &#xE0; l&#x2019;int&#xE9;rieur de ce dernier. Cette interpr&#xE9;tation g&#xE9;om&#xE9;trique simple permet des approximations num&#xE9;riques lorsque les m&#xE9;thodes analytiques ne sont pas envisageables.
Le choix du point &#xE0; l&#x2019;int&#xE9;rieur de chaque sous-intervalle donne lieu &#xE0; diff&#xE9;rentes m&#xE9;thodes. Dans l&#x2019;approximation par l&#x2019;extr&#xE9;mit&#xE9; gauche, la hauteur de chaque rectangle est d&#xE9;termin&#xE9;e par la valeur de la fonction &#xE0; l&#x2019;extr&#xE9;mit&#xE9; gauche du sous-intervalle. Lorsque la fonction est croissante, cette m&#xE9;thode tend &#xE0; sous-estimer l&#x2019;aire totale ; lorsqu&#x2019;elle est d&#xE9;croissante, elle la surestime g&#xE9;n&#xE9;ralement. &#xC0; l&#x2019;inverse, l&#x2019;approximation par l&#x2019;extr&#xE9;mit&#xE9; droite utilise la valeur de la fonction &#xE0; l&#x2019;extr&#xE9;mit&#xE9; droite de chaque sous-intervalle, conduisant &#xE0; une surestimation pour les fonctions croissantes et &#xE0; une sous-estimation pour les fonctions d&#xE9;croissantes.
Ces techniques, bien qu&#x2019;&#xE9;l&#xE9;mentaires dans leur formulation, constituent des outils fondamentaux en analyse num&#xE9;rique. Elles sont particuli&#xE8;rement pr&#xE9;cieuses dans les applications scientifiques et d&#x2019;ing&#xE9;nierie o&#xF9; des int&#xE9;grales doivent &#xEA;tre &#xE9;valu&#xE9;es &#xE0; partir de mesures ponctuelles ou pour des fonctions trop complexes pour l&#x2019;int&#xE9;gration symbolique.

Intégration approximative

Dans de nombreux contextes pratiques et th&#xE9;oriques, la valeur exacte d&#x2019;une int&#xE9;grale d&#xE9;finie peut &#xEA;tre inaccessible. Cette ...

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Techniques of Integration

Techniques d'intégration

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Approximate Integration

riemann sum area estimates

Riemann sums estimate the area under a curve when an exact definite integral is hard to find. This often happens when a function has no known antiderivative or cannot be written in a closed form. It also happens when the function comes from measured data instead of a formula.

The method works by splitting the interval of integration into equal parts. Each subinterval gets a rectangle, and the rectangle height comes from the function value at one chosen point in that part. Adding the rectangle areas gives an approximate integration result.

A left endpoint approximation uses the function value at the left end of each subinterval. For an increasing function, this method usually underestimates the total area. For a decreasing function, it usually overestimates it.

A right endpoint approximation uses the function value at the right end of each subinterval. For an increasing function, it usually overestimates the area. For a decreasing function, it usually underestimates it.

These rectangle-based estimates are simple, but they are useful in numerical analysis. They are especially helpful in science and engineering when an integral must be found from discrete measurements or when symbolic integration is not practical.

Riemann Sum Area Estimates

integration by parts: indefinite integrals

integration-by-parts-indefinite-integrals

Integration by Parts in AC Circuit Analysis

Integration by parts is a calculus method for handling integrals that contain a product of two functions. It is useful when direct integration is not practical. The method comes from the product rule for differentiation, which says that the derivative of a product is the derivative of the first function times the second, plus the first function times the derivative of the second. By integrating that product-rule identity and rearranging the terms, the integration by parts formula is obtained.

integration by parts: definite integrals

Using Parts and Substitution for Area

Integration by parts can make a definite integral easier to solve when the integrand is a product over a fixed interval. The method rewrites the problem as a product at the endpoints minus another definite integral that may be simpler to evaluate. A useful example is the definite integral of inverse tangent, or arctan x. Since there is no direct integration formula for arctan x, the integrand is written as arctan x times the constant function 1. The inverse tangent is chosen to differentiate,...

integration by parts: problem solving

Integration by Parts for Signal Processing

Integration by parts can help evaluate piecewise integrals that appear in signal processing. In smart speakers, audio inputs are modeled as piecewise functions and analyzed with trigonometric functions such as cosine. This lets complex sound waves be broken into simpler frequency parts. When a definite integral uses a piecewise function, the integral is split into separate parts. One part may contain a constant times cosine, which can be found with basic integration rules. Another part may...

integrals of powers of sine and cosine

Solving Trig Integrals with Odd and Even Powers

Trigonometric integrals are solved by looking at the powers of sine and cosine in the expression. These integrals appear often in calculus, and they can also be useful in physics and engineering. For integrals of the form sin^m(x)cos^n(x), the first step is to check whether the sine power or the cosine power is odd. If the sine power is odd, one sine factor is separated from the integrand. That leaves an even power of sine. The remaining sine terms are rewritten using the Pythagorean identity,...

integrals of powers of secant and tangent

integrals-of-powers-of-secant-and-tangent

Solving Secant and Tangent Integrals

Integrals of secant and tangent powers are often solved by choosing a trig substitution that matches the integrand. The key idea is to use the parity of the exponents, which means whether a power is even or odd. A good substitution lets part of the integrand pair with the derivative of a trig function. When the power of secant is even, tangent is the better substitution variable. Since the derivative of tangent is secant squared, a factor of sec^2 x can be split off. The remaining even power...

trigonometric substitution

Finding Ellipse Area with Trig Substitution

Trigonometric substitution is a method for solving integrals that contain square root expressions from quadratic forms. It works well when the integrand looks like a familiar geometric equation, such as a circle or an ellipse. Here, the method is applied to estimate the area inside a Molniya satellite orbit. Molniya satellites move in highly elliptical orbits and repeatedly sweep across the same regions of space as they go around Earth. The orbit is modeled as an ellipse in standard form, and...

integration of rational functions using partial fractions

integration-of-rational-functions-using-partial-fractions

Splitting Rational Integrals Into Simpler Parts

Rational functions are ratios of two polynomials, and their integrals can be simplified by breaking them into smaller parts. A rational function is proper when the degree of the numerator is less than the degree of the denominator. When that is true, partial fraction decomposition rewrites the expression as a sum of simpler rational terms. To decompose a proper rational function, unknown constants are placed into the simpler terms. The denominator is then multiplied through to remove the...

rationalizing substitutions

Integrating Radicals with Rational Substitution

Integrating radicals can be easier when a rationalizing substitution turns the expression into a rational form. This method is useful when standard techniques do not work well because the integrand contains a radical, such as a cube root. The transcript uses a rod as a real-world example. Its linear mass density depends on a constant linear density, a characteristic length, and the distance from the left end of the rod. Finding the total mass means integrating that density over the length of...

approximate integration

Riemann sums estimate the area under a curve when an exact definite integral is hard to find. This often happens when a function has no known antiderivative or cannot be written in a closed form. It also happens when the function comes from measured data instead of a formula. The method works by splitting the interval of integration into equal parts. Each subinterval gets a rectangle, and the rectangle height comes from the function value at one chosen point in that part. Adding the rectangle...

trapezoidal rule

Estimating Distance from Velocity Data

Estimating distance from velocity data is a common use of the trapezoidal rule. In physics and engineering, velocity is often recorded at separate time points instead of as one continuous equation. Numerical integration gives a way to approximate the total displacement from those measurements. The method divides the full time interval into equal parts. For each part, the velocities at the two endpoints are joined with a straight line on a velocity-time graph. That line creates a trapezoid.

simpson's rule i

Estimating Area with Simpson’s Rule

Simpson’s Rule is a numerical integration method for estimating the value of a definite integral. It is useful when an exact antiderivative is hard or impossible to find. The method works by fitting a unique parabola through three equally spaced points on a curve and then integrating that quadratic over the interval. This approach can give a very accurate area estimate from only a few sampled values. It works well for many smoothly varying functions. That makes it a practical tool when a curve...

simpson's rule ii

Simpson's Rule for Curved Sheet Area

Simpson's Rule helps estimate the area under a smooth curve, such as the curved profile of metal roofing sheets. In warehouse roofing, corrugated or curved sheets are used because they add strength, improve water drainage, and support better ventilation. To plan materials and design more accurately, engineers often need the area of these curved surfaces. The sheet shape can often be treated like a parabolic curve because it changes smoothly along its length. That makes numerical integration a...

improper integrals: infinite intervals

Improper Integrals and Exponential Decay

Improper integrals with infinite intervals appear when one limit of integration goes to positive or negative infinity. In that case, the area under the curve is unbounded, so ordinary definite integral methods do not apply directly. The integral is then defined by a limit, which helps show whether the total area is finite even when the interval is infinite. This idea is useful in exponential decay models. One example is the total integrated intensity of light moving through a uniform medium,...

improper integrals: discontinuous integrands

improper-integrals-discontinuous-integrands

Improper Integrals at an Endpoint

Improper integrals can appear when a definite integral has a discontinuity at one endpoint. The integrand may be undefined or become infinite there. In that case, the area under the curve is unbounded near the boundary. This behavior is often linked to a vertical asymptote at the edge of the interval. To evaluate this kind of integral, the endpoint is replaced with a variable. The integral is then written over an interval where the function is defined. After that, a limit is taken as the...

key terms and concepts

Learn how Riemann sums estimate area under a curve using left and right endpoint rectangles when exact integration is not available.

Riemann Sum Area Estimates | JoVE K12

The JoVE Core Calculus collection provides a comprehensive visual guide to the entire calculus sequence, seamlessly connecting mathematical theory to real-world applications in physics and economics. Through dynamic animated lessons, the course transitions smoothly from foundational single-variable concepts to advanced multivariable topics. Students will explore everything from standard differentiation and integration to spatial vectors, multi-dimensional derivatives, and complex vector fields. By breaking down abstract coordinate systems, infinite series, and spatial motion, this structured approach builds the robust analytical skills and advanced mastery essential for STEM success.

calculus

Riemann Sum Area Estimates

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