Name: solving quadratics by factoring and formula
Uploaded: 2025-11-26T05:44:30.000Z
Duration: 1 min 29 s
Channel: JoVE

L’équation du second degré aide à résoudre des problèmes impliquant l’aire lorsqu’une variable apparaît sous la forme d’un terme au carré.Considérons un jardin rectangulaire d’un périmètre de 26 mètres et d’une superficie de 40 mètres carrés. Le but est d’en trouver les dimensions.Soit un côté la variable, en mètres, et exprimons l’autre côté en fonction de cette variable en utilisant la relation de périmètre.En substituant ces expressions dans la formule de l’aire, on obtient un produit impliquant une seule variable.En développant et en réorganisant cette expression, on obtient une équation quadratique.Une méthode pour résoudre cette équation du second degré est la factorisation, où l’équation est écrite comme le produit de deux binômes, chacun mis à zéro pour trouver les valeurs de la variable.Une autre méthode pour résoudre l’équation consiste à compléter le carré. Il s’agit de réécrire l’équation en ajoutant une constante aux deux côtés pour former un carré parfait et en prenant la racine carrée des deux côtés.La formule quadratique est une troisième méthode pour résoudre les équations du second degré. Il s’agit de substituer les coefficients de l’équation dans une formule standard pour trouver les valeurs de la variable.Les trois méthodes donnent les mêmes solutions, qui satisfont les conditions du problème initial.

Équations du second degré

Une &#233;quation du second degr&#233; est une expression alg&#233;brique dans laquelle une variable est &#233;lev&#233;e au carr&#233;, puis combin&#233;e &#224; sa puissance 1 et &#224; une constante, le tout &#233;tant &#233;gal &#224; z&#233;ro. Ces &#233;quations sont fr&#233;quemment utilis&#233;es pour mod&#233;liser des relations faisant intervenir l&#8217;aire, le mouvement ou encore l&#8217;optimisation. La repr&#233;sentation g&#233;n&#233;rale d&#8217;une &#233;quation du second degr&#233; est&#160;:<figure class='image image-style-align-center image_resized' style='display:table;margin-left:auto;margin-right:auto;width:50%;'><img style='aspect-ratio:523/74;' src='https://cloudfront.jove.com/files/ftp_upload/40031/40031_Equation_1_editor_40031.svg' alt='40031_Equation_1.svg' /></figure>o&#249; a, b et c sont des valeurs r&#233;elles, et a est non nul afin de garantir la pr&#233;sence du terme au carr&#233;.L&#8217;une des m&#233;thodes permettant de r&#233;soudre une &#233;quation du second degr&#233; consiste &#224; la r&#233;&#233;crire sous la forme du produit de deux expressions lin&#233;aires. Cette forme factoris&#233;e s&#8217;&#233;crit :<figure class='image image-style-align-center image_resized' style='display:table;margin-left:auto;margin-right:auto;width:50%;'><img style='aspect-ratio:514/74;' src='https://cloudfront.jove.com/files/ftp_upload/40031/40031_Equation_2_editor_40031.svg' alt='40031_Equation_2.svg' /></figure>Dans cette expression, r et s d&#233;signent les valeurs qui annulent chacun des facteurs. D&#8217;apr&#232;s la propri&#233;t&#233; du produit nul, si le produit de deux expressions est nul, alors au moins l&#8217;une d&#8217;entre elles doit &#234;tre nulle. Par cons&#233;quent, les valeurs repr&#233;sent&#233;es par r et s correspondent aux valeurs sp&#233;cifiques de la variable qui satisfont l&#8217;&#233;quation. En rempla&#231;ant l&#8217;une ou l&#8217;autre de ces valeurs dans l&#8217;&#233;quation, on obtient une &#233;galit&#233; v&#233;rifi&#233;e, confirmant ainsi qu&#8217;il s&#8217;agit bien de solutions.Lorsque la factorisation n&#8217;est pas possible, on emploie une m&#233;thode plus g&#233;n&#233;rale consistant &#224; appliquer la formule g&#233;n&#233;rale&#160;:<figure class='image image-style-align-center image_resized' style='display:table;margin-left:auto;margin-right:auto;width:50%;'><img style='aspect-ratio:649/187;' src='https://cloudfront.jove.com/files/ftp_upload/40031/40031_Equation_3_editor_40031.svg' alt='40031_Equation_3.svg' /></figure>Cette formule permet d&#8217;obtenir l&#8217;ensemble des solutions possibles de l&#8217;&#233;quation en substituant les valeurs de a, b et c issues de l&#8217;expression initiale. Le terme situ&#233; sous le signe radical, appel&#233; discriminant, d&#233;termine la nature des solutions. Un discriminant positif conduit &#224; deux solutions distinctes, un discriminant nul &#224; une solution double, et un discriminant n&#233;gatif indique que l&#8217;&#233;quation ne poss&#232;de aucune solution r&#233;elle. Ces m&#233;thodes offrent ainsi une approche compl&#232;te et rigoureuse de la r&#233;solution des &#233;quations du second degr&#233;.

Une &#233;quation du second degr&#233; est une expression alg&#233;brique dans laquelle une variable est &#233;lev&#233;e au carr&#233;, puis ...

Education

Enseignement

JoVE Core

Math Fundamentals

Fondamentaux des mathématiques

Unit

Unité

Foundations of Mathematics

Fondements des mathématiques

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

Quadratic Equations

solving quadratics by factoring and formula

Quadratic equations are algebraic equations with a variable squared, a first-power term, and a constant term. They are set equal to zero. In high school math, they often help model area, motion, and optimization problems.

The general form of a quadratic equation uses real numbers a, b, and c, with a not equal to zero. The nonzero a value keeps the squared term in the equation. One common way to solve a quadratic is to rewrite it as a product of two linear expressions.

In factored form, the equation is written so that the factors contain values r and s. These values make each factor equal to zero. By the zero-product property, if a product equals zero, then at least one factor must be zero. That means r and s are the values of the variable that satisfy the equation, and substituting either value back into the original equation gives a true statement.

When factoring does not work, the quadratic formula gives a more general method. This formula finds all possible solutions by using the values from the original equation. The expression under the square root is called the discriminant. A positive discriminant gives two different real solutions, a zero discriminant gives one repeated solution, and a negative discriminant means there are no real solutions.

Solving Quadratics by Factoring and Formula

solving-quadratics-by-factoring-and-formula

real number system

Number Types on the Real Line

The real number system brings together the number types used for counting, measuring, and comparing quantities. It includes natural numbers, integers, rational numbers, and irrational numbers. Each set adds new kinds of numbers to the same system. Natural numbers are the basic counting numbers: 1, 2, 3, and so on. Integers extend that set by adding zero and negative whole numbers, such as ..., -3, -2, -1, 0, 1, 2, .... Rational numbers are numbers that can be written as a ratio of two...

real number operations

Real Numbers on the Number Line

Real numbers are the values that can be placed on a continuous number line. The system grew from counting numbers used for enumeration. It later expanded to include zero, which shows the absence of quantity, and negative numbers, which are opposites of counting numbers. The real number system also includes fractions and decimals that represent parts of a whole or equal divisions. When written in decimal form, these numbers may end or repeat in a regular pattern. Together, these values describe...

exponents

Exponent Rules and Scientific Notation

Exponents show repeated multiplication in a short form. They are important in algebra and in many other math topics, including scientific computation, scaling laws, and dimensional analysis. For a nonzero real number a and an integer n, a^n means a multiplied by itself n times. Exponent rules help simplify expressions with powers. These properties make it easier to work with exponential expressions in both symbolic and numerical form. They also support common calculations that use exponents in...

radicals

Simplifying Radicals

Radicals show the root of a number and the exponent needed to get that value. A radical expression has two main parts. The radicand is the number inside the root symbol, and the index tells which root to take. The notation n√a means the principal nth root of a. The index changes the type of root. When n equals 2, the expression is a square root. When n equals 3, it is a cube root. The sign of the radicand also matters. If the index is even, a negative radicand does not give a real result. If...

algebraic expressions

Simplifying Algebraic Expressions

Algebraic expressions use variables, constants, and operations to show mathematical relationships. They help describe patterns and solve problems across many areas of mathematics. Knowing the parts of an expression makes it easier to simplify and work with it correctly. Each algebraic expression has separate pieces that work together. A coefficient is the number attached to a variable, and an exponent shows repeated multiplication. Some expressions have a single part, while others include...

rational expressions

Working with Rational Expression Domains

Rational expressions are algebraic fractions with polynomials in the numerator and denominator. They follow the same basic rules as numerical fractions, but variables make them more delicate to work with. A key step is finding values that make the expression undefined, usually because of division by zero or an undefined radical. To determine the domain, start by identifying the values excluded from the denominator. The domain includes all real numbers except those that make the denominator...

linear equations

Solving Linear Equations

Linear equations are a basic algebra tool for modeling constant rates and everyday relationships. They use constants and a single variable, and each term is either a constant or a product of a constant and that variable. When graphed on a Cartesian coordinate plane, they form a straight line that shows a constant rate of change between two quantities. A linear equation in one variable often has the form ax + b = c, where a, b, and c are constants and x is the variable. Solving the equation...

quadratic equations

Quadratic equations are algebraic equations with a variable squared, a first-power term, and a constant term. They are set equal to zero. In high school math, they often help model area, motion, and optimization problems. The general form of a quadratic equation uses real numbers a, b, and c, with a not equal to zero. The nonzero a value keeps the squared term in the equation. One common way to solve a quadratic is to rewrite it as a product of two linear expressions. In factored form, the...

complex numbers

Complex Numbers in Solving Equations

Complex numbers extend the real number system so equations with negative square roots can still be solved. The real numbers cannot represent the square root of a negative number. That limits some quadratic equations, especially those with negative discriminants. To solve this problem, mathematicians introduced the imaginary unit i, where i = √(-1). A complex number is written as x + yi, where x and y are real numbers. In this form, x is the real part and y is the imaginary part. The key rule...

quadratic equations in the complex number system

quadratic-equations-in-the-complex-number-system

Complex Roots of Quadratic Equations

Quadratic equations can have real or complex roots, depending on the discriminant. For an equation in the form ax² + bx + c = 0, the coefficients a, b, and c are the numbers that multiply x², x, and the constant term. The discriminant, b² − 4ac, tells us what kind of solutions to expect. When the discriminant is negative, the equation has no real number solutions. In that case, complex numbers provide a way to continue solving the problem. The imaginary unit i is defined by i = √−1, so a...

radical equations

Solving Radical Equations with Checks

Radical equations are equations with a variable inside a radical, most often a square root or cube root. These equations appear in science, engineering, and real-world measurement problems that involve nonlinear relationships. Solving them starts by isolating the radical expression. Then the radical is removed by raising both sides to the power that matches the radical’s index. This process can create extraneous solutions, which are values that work in the transformed equation but not in the...

inequalities

Solving Inequalities and Interval Notation

Inequalities show how two values compare when they are not equal. They use symbols such as , ≤, and ≥. These statements often describe a range of possible answers instead of one exact value. Interval notation is a shorter way to write these solution sets. An open interval, written as (a, b), leaves out the endpoints. A closed interval, written as [a, b], includes both endpoints. Half-open intervals, such as (a, b] and [a, b), include only one endpoint. Intervals can also extend forever in one...

absolute value inequalities

Absolute Value Inequalities on a Number Line

Absolute value inequalities show how far a number can be from zero or from a target value. Absolute value means distance on the number line, so the sign of the number does not matter. In inequalities, this distance helps define a valid range of values for a variable. An inequality of the form |x| ≤ a, where a ≥ 0, includes every x between −a and a. This can also be written as a compound inequality. On a number line, the solution is shown as a solid segment from −a to a with closed circles at...

mathematical modeling: problem solving

Mathematical Modeling for Loan Payments

Mathematical modeling turns a real-life situation into an equation that can be solved. It starts with defining the problem, choosing measurable quantities, and assigning variables to them. Then a matching model is selected and the equation is solved for the unknown value. This process is especially useful in finance, where models help evaluate investments, loans, and repayment plans. One common example is finding the fixed monthly payment on a loan. That calculation uses the standard annuity...

key terms and concepts

Learn how to solve quadratic equations by factoring or with the quadratic formula, and see how the discriminant shows whether there are real solutions.

Solving Quadratics by Factoring and Formula | JoVE K12

The JoVE Math Fundamentals collection is designed to build a deep and comprehensive understanding of essential mathematics. Covering the foundations of algebra, geometry, trigonometry, and analytic reasoning, this course establishes a strong base for future studies. The collection connects core mathematical concepts with real-world practice, equipping learners to solve complex problems, master problem-solving skills, and apply abstract ideas.

math fundamentals

Solving Quadratics by Factoring and Formula

Description

Transcript

Tags