Name: vertical slices for area between curves
Uploaded: 2026-07-24T11:53:29.280Z
Duration: 1 min 21 s
Channel: JoVE

Considérons deux fonctions continues sur un intervalle fermé [a,b]. La région &#55349 ;&#56390 ; se situe entre les courbes, délimitée verticalement par les fonctions et horizontalement par a et b.La surface entre les courbes peut être estimée en divisant la région en n bandes verticales de largeur égale. Chaque bande est traitée comme un rectangle, utilisé dans la méthode de somme de Riemann.Considérez laième bande. Prenez sa base, puis la hauteur de la bande à xi. La surface de ce rectangle est calculée en multipliant sa hauteur par sa base.L’aire totale estimée de cette courbe est déterminée en additionnant les aires de tous les n rectangles. Ces rectangles ne couvrent pas exactement toute la surface, mais à mesure que le nombre de rectangles augmente et que n tend vers l’infini, la surface totale se rapproche de la surface exacte.Au lieu de sommer les aires des rectangles, l’intégration par rapport à x donne les surfaces de tranches verticales infiniment fines, donnant la surface exacte entre les courbes.Ce concept est utilisé en économie pour déterminer l’écart d’inégalité, qui est l’aire entre la ligne d’égalité parfaite et la courbe de la répartition réelle du revenu.

aire entre deux courbes : intégration par rapport à x

Area Between Curves: Integrating With Respect to x

Consid&#xE9;rez deux fonctions continues d&#xE9;finies sur un intervalle ferm&#xE9; de a &#xE0; b. La r&#xE9;gion comprise entre ces courbes est d&#xE9;limit&#xE9;e verticalement par leurs graphes et horizontalement par les extr&#xE9;mit&#xE9;s de l&#x2019;intervalle. L&#x2019;objectif est de mesurer l&#x2019;aire de cette r&#xE9;gion.Une estimation initiale de l&#x2019;aire peut &#xEA;tre obtenue en divisant l&#x2019;intervalle en un grand nombre de bandes verticales &#xE9;troites de largeur &#xE9;gale. Chaque bande est approxim&#xE9;e par un rectangle dont la hauteur est donn&#xE9;e par la diff&#xE9;rence verticale entre les deux fonctions en un point choisi &#xE0; l&#x2019;int&#xE9;rieur de celle-ci. La somme des aires de ces rectangles fournit une approximation de la r&#xE9;gion sous la forme d&#x2019;une somme de Riemann. Ce processus est donn&#xE9; par\begin{equation*}\text{Area} = \lim_{n \to \infty} \sum_{\textit{i}=1}^{\textit{n}} [ f(x_i) - g(x_i)] \Delta x\end{equation*}&#xA0;Comme les rectangles ne correspondent pas exactement aux bords courbes, cette somme ne fournit qu&#x2019;une approximation lorsqu&#x2019;un nombre fini de bandes est utilis&#xE9;. Toutefois, &#xE0; mesure que le nombre de bandes augmente et que leur largeur diminue, l&#x2019;approximation s&#x2019;am&#xE9;liore. Dans le cas limite, les rectangles deviennent infiniment fins et la somme converge vers l&#x2019;aire exacte.Ce processus de passage &#xE0; la limite remplace la somme de Riemann par une int&#xE9;grale d&#xE9;finie, qui calcule l&#x2019;aire &#xE0; l&#x2019;aide de bandes verticales infiniment fines. L&#x2019;aire exacte comprise entre les courbes est donn&#xE9;e par\begin{equation*}\text{Area} = \int_a^b [ f(x) - g(x) ]\,dx\end{equation*}&#xA0;Cette m&#xE9;thode de d&#xE9;termination de l&#x2019;aire entre deux courbes pr&#xE9;sente des applications importantes au-del&#xE0; des math&#xE9;matiques pures. En &#xE9;conomie, par exemple, l&#x2019;aire comprise entre la droite d&#x2019;&#xE9;galit&#xE9; parfaite et la courbe repr&#xE9;sentant la distribution r&#xE9;elle des revenus est utilis&#xE9;e pour quantifier les in&#xE9;galit&#xE9;s de revenus. L&#x2019;ampleur de cette aire fournit une mesure num&#xE9;rique de l&#x2019;&#xE9;cart d&#x2019;in&#xE9;galit&#xE9;, illustrant ainsi comment des concepts g&#xE9;om&#xE9;triques issus de l&#x2019;analyse peuvent &#xEA;tre appliqu&#xE9;s &#xE0; l&#x2019;analyse &#xE9;conomique du monde r&#xE9;el.

Aire entre deux courbes : intégration par rapport à x

Consid&#xE9;rez deux fonctions continues d&#xE9;finies sur un intervalle ferm&#xE9; de a &#xE0; b. La r&#xE9;gion comprise entre ces courbes est ...

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vertical slices for area between curves

Area between curves can be found by using vertical slices and a definite integral. For two continuous functions on a closed interval from a to b, the region is bounded by their graphs on the sides and by the interval endpoints across the bottom and top edges of the setup.

A first estimate comes from splitting the interval into many narrow vertical strips of equal width. Each strip is treated like a rectangle. Its height is the vertical difference between the two functions at a chosen point inside the strip.

Adding the areas of all the rectangles gives a Riemann sum, which is a way to approximate area with many small pieces. Because the rectangle edges do not exactly follow the curves, the result is only an estimate when the number of strips is finite. As the strips become more numerous and thinner, the approximation improves.

In the limiting case, the strips become infinitely thin. Then the Riemann sum becomes a definite integral, which gives the exact area using infinitely thin vertical slices. This method is useful beyond pure math. In economics, the area between the line of perfect equality and a curve showing actual income distribution can be used to measure income inequality. The size of that area gives a numerical value for the inequality gap.

Vertical Slices for Area Between Curves

area between curves: integrating with respect to x

Area between curves can be found by using vertical slices and a definite integral. For two continuous functions on a closed interval from a to b, the region is bounded by their graphs on the sides and by the interval endpoints across the bottom and top edges of the setup. A first estimate comes from splitting the interval into many narrow vertical strips of equal width. Each strip is treated like a rectangle. Its height is the vertical difference between the two functions at a chosen point...

area between curves: integrating with respect to y

area-between-curves-integrating-with-respect-to-y

Horizontal Slices for Area Between Curves

Area between curves can be found with horizontal slices when both boundaries are written as functions of y. The left and right curves are continuous from y = c to y = d, and those lines set the vertical limits of the region. Because the curves depend on y, the area is best measured by moving across the shape with thin horizontal strips. The method uses a Riemann sum. The region is divided into many thin strips with the same height, delta y. For each strip, the width is the horizontal distance...

area between curves: problem solving

Piecewise Area Between Curves

Piecewise area between curves uses more than one integral to find the size of a region on a graph. In this example, the region is enclosed by a square root function, a reflected cube root function, and a linear function. The line intersects each of the other two curves, and those intersection points show where the boundary of the region changes. The area cannot be found with one setup over the full interval because the top and bottom curves are not the same everywhere. The region is split at...

calculation of volume of solids by integration

calculation-of-volume-of-solids-by-integration

Slicing Methods for Solid Volume

Slicing methods help find the volume of solids with changing cross-sections. A basic solid, like a rectangular box, is easy to measure because its base area stays the same along its height. Many real objects do not have that regular shape, so elementary geometry is not enough. The slicing method solves this by breaking a solid into many very thin slices. These slices are taken perpendicular to a chosen axis, often the x-axis. Each slice has a small thickness, written as delta x, and a...

volumes of solids of revolution

Disk Method for Rotated Region Volume

The disk method is used to find the volume of a solid formed by rotating a region around an axis. The region is first drawn in a two-dimensional plane. When that region spins around a fixed line, called the axis of revolution, it creates a three-dimensional shape with rotational symmetry. These shapes appear often in math models, physics, and engineering. When the region touches the axis of revolution, the solid has no hollow space inside. Its cross-sections are circular, so the shape can be...

finding volume using cross-sectional area

finding-volume-using-cross-sectional-area

Tetrahedron Volume from Triangle Slices

Tetrahedron volume can be found by adding the areas of triangular slices. This method uses cross-sectional area, which is the area of a flat slice taken through a 3D solid. It is useful when a solid changes shape in a regular way and a simple geometric formula is not available. A tetrahedron is a good example. It has a height h and an equilateral triangle base with side length a. The coordinate system places the origin at the top vertex, and the y-axis goes downward along the height to the...

problem solving: volume

Finding the Volume of a Jet Fuel Tank

The volume of a jet fuel tank can be found with solids of revolution. The tank is modeled by rotating a two-dimensional region around the x-axis. This creates a three-dimensional shape that is symmetric about the axis of rotation. The region runs from 0 to 2 meters, so the tank’s shape can be measured along that length. Because the boundary curve touches the axis, the disk method works well here. The disk method breaks the solid into many very thin circular slices that are perpendicular to the...

average value of a function

Estimating Function Behavior with Average Value

The average value of a function gives one number that summarizes how a quantity changes over a closed interval. It can also be viewed as the height of a rectangle whose area matches the net area under the curve. That net area includes both positive and negative parts of the function, so the result reflects the function’s overall behavior. A greenhouse temperature over a 24-hour period is a practical example of this idea. The temperature may rise and fall throughout the day, but it is still...

key terms and concepts

Learn how vertical strips and Riemann sums lead to a definite integral for finding area between curves, plus a real-world example from economics.

Vertical Slices for Area Between Curves | 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

Vertical Slices for Area Between Curves

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