Name: using derivatives to read a graph
Uploaded: 2026-01-12T12:24:56.000Z
Duration: 1 min 22 s
Channel: JoVE

Considérons une fonction ; ses première et deuxième dérivées sont utilisées pour esquisser sa courbe.La première dérivée est nulle lorsque x est égal à quatre, et indéfinie lorsque x est égal à zéro ou x égal à six. Ces points critiques définissent les intervalles d’analyse.Le signe de la première dérivée détermine si la courbe est croissante ou décroissante.Un changement de signe de négatif à positif en x égal à zéro donne un minimum local.Un changement de positif à négatif à x égal à quatre donne un maximum local. Si le signe ne change pas en x égal à six, il n’existe pas d’extremum à cet endroit.La dérivée seconde est négative sur les intervalles de moins infini à 0 et de 0 à 6, ce qui montre que le graphique est concave vers le bas sur ces intervalles.Mais la dérivée seconde est positive sur l’intervalle x supérieur à six, ce qui donne le graphique ascendant concave sur cet intervalle.Par exemple, considérons une fonction de profit. La première dérivée suit la montée ou la baisse du profit et identifie ses valeurs extrêmes.La seconde dérivée montre comment le taux de profit évolue, ce qui aide à esquisser la fonction.

tracé de courbes et dérivation

Curve Sketching and Derivatives

Comprendre le comportement d&#x2019;une fonction &#xE0; travers ses d&#xE9;riv&#xE9;es premi&#xE8;re et seconde est essentiel pour analyser sa repr&#xE9;sentation graphique. Les d&#xE9;riv&#xE9;es permettent de d&#xE9;terminer les intervalles sur lesquels la fonction cro&#xEE;t ou d&#xE9;cro&#xEE;t, d&#x2019;identifier les points o&#xF9; elle atteint des maxima ou des minima locaux, ainsi que la mani&#xE8;re dont sa courbure &#xE9;volue selon les diff&#xE9;rents intervalles.La d&#xE9;riv&#xE9;e premi&#xE8;re d&#x2019;une fonction renseigne sur la pente de la droite tangente en tout point. Les points pour lesquels la d&#xE9;riv&#xE9;e est nulle ou ind&#xE9;finie sont appel&#xE9;s points critiques, car ils indiquent souvent la pr&#xE9;sence potentielle d&#x2019;extr&#xE9;mums ou de changements de comportement. Un minimum local se produit lorsque la d&#xE9;riv&#xE9;e premi&#xE8;re passe de n&#xE9;gative &#xE0; positive, tandis qu&#x2019;un maximum local appara&#xEE;t lorsqu&#x2019;elle passe de positive &#xE0; n&#xE9;gative. Si la d&#xE9;riv&#xE9;e ne change pas de signe en un point critique, aucun extr&#xE9;mum ne se pr&#xE9;sente.La d&#xE9;riv&#xE9;e seconde fournit des informations sur la concavit&#xE9; de la fonction. Lorsque la d&#xE9;riv&#xE9;e seconde est n&#xE9;gative, la courbe est concave vers le bas, ce qui indique que la pente de la d&#xE9;riv&#xE9;e premi&#xE8;re diminue. La courbe se courbe alors vers le bas. &#xC0; l&#x2019;inverse, une d&#xE9;riv&#xE9;e seconde positive signifie que la fonction est concave vers le haut, ce qui correspond &#xE0; une pente de la d&#xE9;riv&#xE9;e premi&#xE8;re qui augmente et &#xE0; une courbe qui s&#x2019;incurve vers le haut. Les changements de concavit&#xE9; sugg&#xE8;rent la pr&#xE9;sence de points d&#x2019;inflexion, o&#xF9; la nature de la courbe passe d&#x2019;un type de concavit&#xE9; &#xE0; un autre.En examinant les signes et le comportement des d&#xE9;riv&#xE9;es premi&#xE8;re et seconde sur diff&#xE9;rents intervalles, il est possible de construire une esquisse fid&#xE8;le de la fonction. Cette approche combin&#xE9;e permet d&#x2019;identifier les zones d&#x2019;augmentation ou de diminution, de localiser les maxima et minima locaux, et de d&#xE9;terminer la forme g&#xE9;n&#xE9;rale de la repr&#xE9;sentation graphique de la fonction.ApplicationsPar exemple, consid&#xE9;rons un mod&#xE8;le de b&#xE9;n&#xE9;fice repr&#xE9;sent&#xE9; par une fonction quadratique : \begin{equation} P(x) = -2x^2 + 12x - 10 \end{equation}Le graphique repr&#xE9;sente une courbe de b&#xE9;n&#xE9;fice, o&#xF9; x d&#xE9;signe les d&#xE9;penses publicitaires exprim&#xE9;es en milliers de dollars am&#xE9;ricains, et P(x) repr&#xE9;sente le b&#xE9;n&#xE9;fice, &#xE9;galement exprim&#xE9; en milliers de dollars am&#xE9;ricains. La courbe adopte une forme en U invers&#xE9;, &#xE9;voquant une colline. En termes math&#xE9;matiques, cette forme est d&#xE9;crite comme concave vers le bas.&#xC0; de faibles niveaux de d&#xE9;penses publicitaires, l&#x2019;augmentation des d&#xE9;penses accro&#xEE;t efficacement les ventes et le b&#xE9;n&#xE9;fice. Toutefois, &#xE0; mesure que les d&#xE9;penses continuent d&#x2019;augmenter, le b&#xE9;n&#xE9;fice suppl&#xE9;mentaire g&#xE9;n&#xE9;r&#xE9; par chaque unit&#xE9; additionnelle de publicit&#xE9; commence &#xE0; diminuer. Ce ph&#xE9;nom&#xE8;ne illustre le principe des rendements d&#xE9;croissants. Si les d&#xE9;penses deviennent excessives, le b&#xE9;n&#xE9;fice finit par diminuer, car le co&#xFB;t de la publicit&#xE9; suppl&#xE9;mentaire d&#xE9;passe les revenus qu&#x2019;elle g&#xE9;n&#xE8;re.La pente de la courbe est donn&#xE9;e par la d&#xE9;riv&#xE9;e premi&#xE8;re, et le b&#xE9;n&#xE9;fice maximal est atteint au point o&#xF9; cette pente devient nulle. &#xC0; ce niveau de d&#xE9;penses, la courbe atteint sa valeur la plus &#xE9;lev&#xE9;e.La d&#xE9;riv&#xE9;e seconde de la fonction est une constante n&#xE9;gative. Une d&#xE9;riv&#xE9;e seconde n&#xE9;gative indique que l&#x2019;ensemble de la courbe est concave vers le bas, ce qui confirme que la fonction de b&#xE9;n&#xE9;fice se courbe vers le bas en tout point.

Tracé de courbes et dérivation

Comprendre le comportement d&#x2019;une fonction &#xE0; travers ses d&#xE9;riv&#xE9;es premi&#xE8;re et seconde est essentiel pour analyser sa ...

Education

Enseignement

JoVE Core

Calculus

Calcul

Unit

Unité

Applications of Differentiation

Applications de la dérivation

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

using derivatives to read a graph

Derivatives help students read the graph of a function by showing where the graph rises, falls, and bends. The first derivative tells the slope of the tangent line at each point. The second derivative shows how the curve changes shape over an interval.

Points where the first derivative is zero or undefined are critical points. These points are important because they may mark a local maximum, a local minimum, or no extremum at all. A local minimum appears when the first derivative changes from negative to positive. A local maximum appears when it changes from positive to negative.

If the first derivative does not change sign at a critical point, then the function does not have an extremum there. The second derivative adds information about concavity, which describes whether the graph bends upward or downward. A negative second derivative means the graph is concave downward. A positive second derivative means the graph is concave upward.

When the second derivative is negative, the slope of the first derivative is decreasing, so the curve bends downward. When the second derivative is positive, the slope of the first derivative is increasing, so the curve bends upward. A change in concavity can signal an inflection point, where the graph switches from one type of bending to the other.

By checking the signs of the first and second derivatives on different intervals, students can sketch a function more accurately. This process identifies where the function increases or decreases, where it has local maxima and minima, and how its overall shape develops. The same ideas apply to a quadratic profit model where x is advertising spend in thousands of USD and P(x) is profit in thousands of USD.

In that example, the graph looks like a hill, or an inverted U shape. That shape is concave downward, so the profit curve bends downward throughout. At low advertising levels, more spending raises sales and profit efficiently. As spending keeps rising, the extra profit from each additional unit of advertising gets smaller, which shows diminishing returns.

If advertising becomes too high, profit can start to fall because the cost of the extra advertising is greater than the revenue it brings in. The maximum profit occurs where the first derivative is zero, because the slope of the curve becomes flat there. The second derivative is a constant negative number, which confirms that the entire profit function is concave downward.

Using Derivatives to Read a Graph

absolute and local extreme values

Finding Max and Min on Function Graphs

Absolute and local extreme values show the highest and lowest points on a function graph. Absolute maximum and absolute minimum values describe the highest and lowest values across the entire domain. Local maximum and local minimum values describe the highest and lowest values within a smaller part of the graph. Periodic functions such as sine and cosine can have extreme values at many points. Their repeating pattern creates multiple local extrema. In these cases, the derivative becomes zero...

critical numbers and the closed interval method

critical-numbers-and-the-closed-interval-method

Finding Absolute Extrema on a Closed Interval

Absolute extrema on a closed interval are found by checking critical numbers and the endpoints. A function’s maximum and minimum values help describe its overall behavior across its domain. These values are called extrema, and they can be local or absolute. Local extrema are peaks and valleys in a limited region. Absolute extrema are the highest or lowest points on the entire interval. Critical numbers are the domain values where the derivative is zero or does not exist. According to Fermat’s...

rolle’s theorem

Rolle’s Theorem and Zero Slope Points

Rolle’s Theorem explains when a differentiable function must have a flat tangent inside an interval. It applies to a real-valued function on a closed interval, which means the endpoints are included. The function must also be continuous on the whole interval and differentiable on the open interval, where the interior points lie. The theorem uses one more key condition. The function must have the same value at both endpoints. When that happens, Rolle’s Theorem guarantees at least one point...

the mean value theorem

Mean Change and Instantaneous Slope

The Mean Value Theorem links average change to instantaneous slope. It shows that when a function changes smoothly over an interval, the average change across the whole interval must match the change at one specific point inside it. The theorem is easy to see in a motion example. Imagine a vehicle traveling between two points on a road. Its velocity can change during the trip, beginning slowly, speeding up during acceleration, and slowing down near the end. Even when the speed is not...

first derivatives and the shape of a graph

first-derivatives-and-the-shape-of-a-graph

Using First Derivatives to Find Graph Changes

The first derivative shows how a function changes across its domain. In calculus, the derivative is written as f'(x). It tells us whether the graph is rising, falling, or turning at a given point. A function is increasing on an interval when its derivative is positive. That means the slope of the tangent line is positive. A function is decreasing on an interval when its derivative is negative. In that case, the tangent line slopes downward. These sign changes help describe the overall shape...

first derivative test: problem solving

Finding Turning Points with the First Derivative

The first derivative test is used to find turning points on a smooth curve. It shows where a function changes from increasing to decreasing, or from decreasing to increasing. In this example, the curve can model an asset price that falls to a low point, rebounds, and then gradually declines again. The process starts by finding the first derivative of the function. Because the function is a product of a polynomial term and an exponential term, the product rule is needed. After differentiating,...

second derivatives and the shape of a graph

second-derivatives-and-the-shape-of-a-graph

Using Second Derivatives to Read Curvature

The second derivative shows how a graph bends. It gives key information about curvature and how that curvature changes over an interval. These ideas help with graph analysis in math and in real-world settings such as road elevation, population growth, and economic trends. A function f(x) is concave upward on an interval when its graph lies above all of its tangent lines. In this case, the second derivative is positive. That means the slope of the tangent line is increasing, and the graph bends...

second derivative test: problem solving

Classifying Critical Points with the Second Derivative

The second derivative test helps classify critical points of a function. Critical points are places where the first derivative is zero or undefined. They are possible locations for local maxima and local minima, but they do not always become one or the other. The second derivative shows concavity, or whether a graph bends up or down. If f''(x) &gt; 0, the function is concave up, and the critical point is a local minimum. If f''(x) &lt; 0, the function is concave down, and the critical point is...

curve sketching and derivatives

Derivatives help students read the graph of a function by showing where the graph rises, falls, and bends. The first derivative tells the slope of the tangent line at each point. The second derivative shows how the curve changes shape over an interval. Points where the first derivative is zero or undefined are critical points. These points are important because they may mark a local maximum, a local minimum, or no extremum at all. A local minimum appears when the first derivative changes from...

indeterminate forms and l’hôpital’s rule

Using Derivatives to Resolve Limit Ambiguity

Indeterminate forms appear when a limit gives an expression that cannot be read directly. Common examples are 0 divided by 0 and infinity divided by infinity. These results do not show the true behavior of the function near the point of interest, so more analysis is needed. L’Hôpital’s Rule is a useful method for handling these ambiguous limits. It applies when two differentiable functions approach 0 or infinity at the same time near the point being studied. Instead of finding the limit of the...

indeterminate products

Limits of Zero Times Infinity

Limits with a zero-times-infinity product are indeterminate. In this type of limit, one factor approaches zero while the other factor grows toward positive or negative infinity. The result is not obvious at first, because the product may approach zero, infinity, or a finite nonzero value. To evaluate these product limits, the expression is first rewritten as a quotient. This form makes it possible to use L'Hôpital's Rule, which compares the derivatives of the numerator and denominator. A...

guidelines for sketching a curve

Using Derivatives to Sketch Function Graphs

Sketching a function graph uses key features of the function to show its overall shape. A function plots as a curve on the coordinate plane, with the input on the horizontal axis and the output on the vertical axis. The first step is to find the domain, which is the set of input values where the function is defined. The domain shows how far the graph can extend left and right. Intercepts are also important reference points. The x-intercept is where the graph crosses the horizontal axis, and...

slant asymptotes

Rational Functions with Slant Asymptotes

Rational functions can follow a slant asymptote when the numerator grows faster than the denominator. In this case, a cubic numerator is divided by a squared denominator. That degree difference creates a linear trend that guides the graph at large input values. The function is only defined where the denominator is not zero. Those excluded x-values split the domain into separate regions and avoid singular points. The graph can still cross the x-axis where the numerator equals zero, so the real...

optimization problems

Pipe Length Around a Corner

Pipe length around a corner is a classic constrained optimization problem. It shows how calculus can find a maximum or minimum value when space is limited by fixed walls and angles. The example used here asks for the longest horizontal pipe that can move around a right-angled turn. One hallway is 3 meters wide and the other is 2 meters wide. The pipe is shown as a straight line that touches the inner corner and reaches the opposite walls of both hallways. The key idea is that the pipe’s...

application of differentiation to business

application-of-differentiation-to-business

Maximizing Bakery Revenue with Calculus

Calculus helps businesses make pricing decisions that can improve revenue. In this example, a bakery uses a cupcake model to find the best price and daily sales volume. The goal is to see how changes in price affect demand and total revenue. The demand function shows the link between price and how many cupcakes are sold each day. In this model, p(x) gives the price per cupcake when x cupcakes are sold. Lower prices lead to higher demand, so the function captures how sales change with price. <br...

newton’s method

Newton’s Method for Finding Roots

Newton’s Method is an iterative way to find the roots of real-valued, differentiable functions. A root is the value of x that makes a function equal to zero. This method is useful when an exact algebraic answer is hard to find. The process starts with an initial guess. Newton’s Method then uses the function value and its derivative, which is the slope of the function at that point, to build a better estimate. The next approximation is found from the recursive formula x n+1 = x n - f(x n) /...

the antiderivative of a function

Finding Original Functions with Antiderivatives

Antiderivatives help reconstruct an original function from its derivative. In calculus, an antiderivative of a function f(x) is a function F(x) whose derivative gives back f(x). This idea works like reversing differentiation to recover the starting form. Antiderivatives are not unique because differentiation removes constant terms. For that reason, the general form includes an arbitrary constant C. That constant represents unknown initial conditions when a function is rebuilt from its...

graphing antiderivatives

Antiderivative Graph Shape and Slope

Antiderivative graphs show how a function accumulates over time. In calculus, an antiderivative tracks that buildup, much like the changing position of a rolling ball as its velocity changes. The graph of the antiderivative reflects the total effect of the original function's values. The sign of the original function helps determine the antiderivative's direction. When the function is positive, the antiderivative rises because the accumulation grows. When the function is negative, the...

application of antiderivatives: linear motion

application-of-antiderivatives-linear-motion

Finding Car Stopping Distance with Integration

Integration connects acceleration, velocity, and displacement in linear motion. It works as the reverse of a derivative, which tells how one quantity changes with another. In physics, this makes it possible to move from a rate of change back to the motion itself. A car provides a clear example. It is moving at a steady 20 meters per second when an obstacle appears 800 meters ahead. To stop in time, the car slows with a constant acceleration. That acceleration tells how the car’s velocity...

key terms and concepts

Learn how the first and second derivatives reveal increase, decrease, local maxima, minima, concavity, and inflection points in function graphs.

Using Derivatives to Read a Graph | 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

Using Derivatives to Read a Graph

Description

Transcript

Tags