Name: solving trigonometric equations
Uploaded: 2025-11-26T05:44:20.000Z
Duration: 1 min 30 s
Channel: JoVE

Une équation trigonométrique implique une ou plusieurs fonctions trigonométriques d’un angle inconnu, généralement mesurées en radians. Certaines de ces équations sont des identités, vraies pour toutes les valeurs d’angle, tandis que d’autres ne sont valides que pour des angles spécifiques.Les fonctions trigonométriques telles que le sinus, le cosinus et la tangente sont périodiques, ce qui signifie que leurs valeurs se répètent à intervalles réguliers. Le sinus et le cosinus ont une période de 2π, tandis que la tangente a une période de π. L’addition des multiples entiers de cette période donne toutes les solutions.Par exemple, résoudre une équation trigonométrique de type quadratique revient à résoudre une équation trigonométrique standard. L’équation est factorisée, chaque facteur étant égal à zéro pour trouver l’angle correspondant.Après avoir identifié des solutions dans un intervalle primaire, par exemple de 0 à 2π pour le sinus, l’ensemble complet de solutions comprend toutes les valeurs équivalentes obtenues en ajoutant des multiples entiers de la période de la fonction.Ce concept apparaît dans les oscillations pendulaires, où le déplacement angulaire varie sinusoïdalement avec le temps. L’équation correspondante décrit comment ce déplacement dépend du temps. La résolution de cette équation trigonométrique permet de prédire le moment où le pendule passe par le centre ou atteint ses extrêmes.

Équations trigonométriques

Trigonometric Equations

Les &#233;quations trigonom&#233;triques impliquent une ou plusieurs fonctions trigonom&#233;triques et apparaissent fr&#233;quemment en mod&#233;lisation math&#233;matique. Ces &#233;quations peuvent &#234;tre des identit&#233;s, valables pour toutes les valeurs de la variable, ou des &#233;quations conditionnelles, valables uniquement pour certaines valeurs. La r&#233;solution des &#233;quations trigonom&#233;triques mobilise g&#233;n&#233;ralement des techniques alg&#233;briques ainsi que les propri&#233;t&#233;s fondamentales des fonctions trigonom&#233;triques.Certaines &#233;quations trigonom&#233;triques ressemblent &#224; des formes alg&#233;briques usuelles et peuvent &#234;tre r&#233;solues &#224; l&#8217;aide de techniques telles que la factorisation. Prenons, par exemple, l&#8217;&#233;quation trigonom&#233;trique de type quadratique :<figure class='image image-style-align-center image_resized' style='display:table;margin-left:auto;margin-right:auto;width:50%;'><img style='aspect-ratio:1920/120;' src='https://cloudfront.jove.com/files/ftp_upload/40080/40080_Equation_1_1__editor_40080.svg' alt='40080_Equation_1_1_.svg' /></figure>Dans ce cas, le membre de gauche est un polyn&#244;me du second degr&#233; en sin x. La factorisation du trin&#244;me donne :<figure class='image image-style-align-center image_resized' style='display:table;margin-left:auto;margin-right:auto;width:50%;'><img style='aspect-ratio:1920/120;' src='https://cloudfront.jove.com/files/ftp_upload/40080/40080_Equation_2_1__editor_40080.svg' alt='40080_Equation_2_1_.svg' /></figure>Cela conduit &#224; deux &#233;quations possibles :<figure class='image image-style-align-center image_resized' style='display:table;margin-left:auto;margin-right:auto;width:50%;'><img style='aspect-ratio:1920/120;' src='https://cloudfront.jove.com/files/ftp_upload/40080/40080_Equation_3_1__editor_40080.svg' alt='40080_Equation_3_1_.svg' /></figure>Comme le sinus de tout angle r&#233;el appartient &#224; l&#8217;intervalle [&#8722;1, 1], l&#8217;&#233;quation sin x = 2 n&#8217;a pas de solution. En revanche, l&#8217;&#233;quation sin x = 1 admet des solutions. Dans l&#8217;intervalle [0, 2&#960;), la valeur sin x = 1 est atteinte pour :<figure class='image image-style-align-center image_resized' style='display:table;margin-left:auto;margin-right:auto;width:50%;'><img style='aspect-ratio:1920/250;' src='https://cloudfront.jove.com/files/ftp_upload/40080/40080_Equation_4_1__editor_40080.svg' alt='40080_Equation_4_1_.svg' /></figure>En tenant compte de la p&#233;riodicit&#233; de la fonction sinus, l&#8217;ensemble des solutions s&#8217;exprime ainsi&#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:1920/250;' src='https://cloudfront.jove.com/files/ftp_upload/40080/40080_Equation_5_1__editor_40080.svg' alt='40080_Equation_5_1_.svg' /></figure>o&#249; k est un entier quelconque.Dans les cas impliquant plusieurs fonctions trigonom&#233;triques ou plusieurs angles, on utilise des identit&#233;s usuelles pour r&#233;&#233;crire l&#8217;&#233;quation en termes d&#8217;une seule fonction, ce qui permet d&#8217;appliquer des m&#233;thodes de r&#233;solution alg&#233;briques. Lorsque la fonction est &#233;gale &#224; une valeur non remarquable, les fonctions r&#233;ciproques (arcsinus, arccosinus, arctangente) permettent de d&#233;terminer l&#8217;angle, la prise en compte des quadrants garantissant une interpr&#233;tation correcte. Les m&#233;thodes graphiques sont &#233;galement utiles : elles mettent en &#233;vidence les points d&#8217;intersection, confirment visuellement les solutions alg&#233;briques et illustrent la nature p&#233;riodique des fonctions.

Les &#233;quations trigonom&#233;triques impliquent une ou plusieurs fonctions trigonom&#233;triques et apparaissent fr&#233;quemment en mod&#233;lisation ...

Education

Enseignement

JoVE Core

Math Fundamentals

Fondamentaux des mathématiques

Unit

Unité

Trigonometry

Trigonométrie

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

solving trigonometric equations

Trigonometric equations use one or more trigonometric functions, and they often appear in mathematical modeling. Some are identities, which are true for every value of the variable. Others are conditional equations, which are true only for specific values.

Solving these equations usually combines algebra with the basic properties of trigonometric functions. Some equations look like standard algebra problems, so factoring can work well. For example, a quadratic form in sin x can be factored into simpler equations.

That step may produce two separate equations. One may have no solution because sine for a real angle stays within the range [−1,1]. The other may have valid solutions. For example, sin x = 1 occurs at x = π/2 in the interval [0, 2π), and the periodic nature of sine gives the full set of solutions as x = π/2 + 2kπ, where k is any integer.

When an equation contains more than one trigonometric function or more than one angle, identities help rewrite it in terms of a single function. The equation can then be solved with algebraic methods. If the function equals a non-standard value, inverse trigonometric functions help find the angle, and quadrant checks show the correct solution. Graphs also help by showing where the curves intersect and by highlighting the periodic behavior of the functions.

Solving Trigonometric Equations

radian and degree measure

Degrees to Radians in Circle Measure

Degrees and radians are the two main units used to measure angles. They both describe rotation around a fixed point. A full turn equals 360 degrees or 2π radians, depending on the unit used. Degrees divide a circle into 360 equal parts. This makes them easy to use in everyday math. They are common in navigation, design, and basic geometry. Radians come from the geometry of a circle. One radian is the angle made when the arc length matches the radius of the circle. Since a circle’s...

trigonometric functions of real numbers

Unit Circle Trig: Signs and Symmetry

The unit circle is the basis for trigonometric functions on real numbers. It is a circle with radius one centered at the origin of the coordinate plane. On this circle, arc length means the distance measured along the circumference between two points. Each real number t is shown as an arc length measured counterclockwise from the positive x-axis. A point on the unit circle has coordinates (x, y). These coordinates define cosine and sine. The x-coordinate equals cos t, and the y-coordinate...

graphs of trigonometric functions

Trigonometric Wave Graphs and Asymptotes

Trigonometric functions create repeating waves and curved graphs with clear symmetry. Their shapes come from the unit circle, where a point moves counterclockwise and its vertical and horizontal positions form the sine and cosine values. Sine and cosine graphs are smooth waves with the same period, or repeat length. Their ranges stay bounded between -1 and 1. Sine, cosine, and the other trig functions all show regular patterns, but each one has its own graph shape. Tangent is the ratio of...

trigonometry of right triangles

Trig Ratios for Right Triangle Sides

Right triangle trigonometry uses sine, cosine, and tangent to connect an acute angle with the sides of the triangle. These trig ratios describe how side lengths relate to one another in right-angled geometry. They give a clear way to measure the links between angles and sides. Sine compares the side opposite an angle to the hypotenuse. Cosine compares the side adjacent to the angle to the hypotenuse. Tangent compares the opposite side to the adjacent side. Each ratio depends on the angle, not...

trigonometric functions: problem solving

Measuring Rocket Height with Trigonometry

Measuring rocket height with trigonometry uses a fixed ground point and a changing angle of elevation. An observer stands a known horizontal distance from the launch site and watches the object rise. The angle between the ground and the line of sight gives the key information for finding height. The tangent function is the main tool for this calculation. Tangent is the ratio of the vertical side to the adjacent side in a right triangle. When the ground distance is fixed, the object’s height...

the law of sines

Solving Oblique Triangles with Sines

Solving oblique triangles uses the Law of Sines. An oblique triangle is a triangle with no right angle. These triangles need a different trigonometric method because the Pythagorean theorem works only for right triangles. The Law of Sines links each side of a triangle to the sine of its opposite angle. In triangle ABC, side a is opposite angle A, side b is opposite angle B, and side c is opposite angle C. The ratios a/sin A, b/sin B, and c/sin C are constant. This relationship helps find...

the law of cosines

Using Cosines to Find Triangle Sides

The Law of Cosines helps find unknown sides and angles in any triangle. It is a key trig formula for non-right triangles, where the Pythagorean Theorem does not give a direct answer. The law links side lengths to the cosine of an angle, so students can solve triangles with missing measurements. For a triangle with sides a, b, and c and opposite angles A, B, and C, the formula is written as a squared equals b squared plus c squared minus 2bc cosine A. Similar equations can be used for the other...

trigonometric identities i

Unit Circle Trig Identities and Sum Formulas

Trigonometric identities link trigonometric functions and stay true for every angle in their domains. A key example is the Pythagorean identity, which comes directly from the geometry of the unit circle. For an angle θ, a point on the unit circle has coordinates (cos θ, sin θ). Because the radius is 1, the Pythagorean Theorem gives the basic identity. That same identity can be rearranged to create another useful form. If it is divided by cos²θ, assuming cos θ is not 0, it leads to a second...

trigonometric identities ii

Double-Angle and Half-Angle Formulas

Double-angle and half-angle trigonometric formulas connect angles that are multiplied or divided by two. They come from the sum and difference formulas, so they build on earlier trigonometry skills. These identities help simplify expressions, solve equations, and evaluate integrals. The double-angle formulas come from substituting equal angles into the sum formulas. For sine and cosine, they link the value at 2θ to the value at θ. The tangent double-angle identity follows the same idea. These...

trigonometric identities iii

Cofunction Identities and Complementary Angles

Cofunction identities show how trigonometric functions change for complementary angles. Complementary angles add up to 90°. These identities are a useful part of trigonometry for grades 9–12. The idea becomes clear on the unit circle. Every angle θ, measured counterclockwise from the positive x-axis, matches a point with coordinates (cos θ, sin θ). The cosine gives the horizontal component, and the sine gives the vertical component of the terminal side. The same point can also be described...

inverse trigonometric functions

Inverse Trig Functions and Angle Finding

Inverse trigonometric functions are used to find angles from trig ratios. Standard trigonometric functions turn angles into ratios, while inverse trigonometric functions reverse that process and map a ratio back to its angle. That makes them useful whenever a problem gives distances or side lengths instead of an angle. A function must be one-to-one to have a valid inverse. This means each input must match only one output. Trigonometric functions are not naturally one-to-one over their full...

trigonometric equations

Trigonometric equations use one or more trigonometric functions, and they often appear in mathematical modeling. Some are identities, which are true for every value of the variable. Others are conditional equations, which are true only for specific values. Solving these equations usually combines algebra with the basic properties of trigonometric functions. Some equations look like standard algebra problems, so factoring can work well. For example, a quadratic form in sin x can be factored...

key terms and concepts

Learn how to solve trigonometric equations using factoring, identities, inverse trig functions, and graphs. Built for high school math students.

Solving Trigonometric Equations | 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 Trigonometric Equations

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