Trigonometric ratios

Trigonometric ratios form the foundation of trigonometry, a branch of mathematics that explores the relationships between the angles and sides of triangles. In this tutorial, we will delve into the fundamental trigonometric ratios—sine, cosine, and tangent—and understand how they are defined, calculated, and applied.

1. Basic Concepts

a. Right-Angled Triangles:

Trigonometry is primarily concerned with right-angled triangles. A right-angled triangle has one angle measuring 90 degrees (a right angle).

b. Hypotenuse, Opposite, and Adjacent:

  • Hypotenuse (H): The side opposite the right angle.
  • Opposite (O): The side opposite the angle under consideration.
  • Adjacent (A): The side adjacent to and not the hypotenuse.

2. Trigonometric Ratios:

Trigonometric ratios are fundamental concepts in mathematics, specifically in trigonometry, which is the branch of mathematics that deals with the relationships between the angles and sides of triangles. The three primary trigonometric ratios are sine (sin), cosine (cos), and tangent (tan). These ratios are defined based on the sides of a right-angled triangle and are used to relate angles within the triangle.

Let’s explore each trigonometric ratio in detail:

a. Sine (sin):

The sine of an angle in a right-angled triangle is the ratio of the length of the side opposite the angle to the length of the hypotenuse.

\(sin(\theta)=\frac{Opposite side}{Hypotenuse}\)

b. Cosine (cos):

The cosine of an angle is the ratio of the length of the adjacent side to the length of the hypotenuse.

\(cos(\theta)=\frac{Adjacent side}{Hypotenuse}​\)

c. Tangent (tan):

The tangent of an angle is the ratio of the length of the side opposite the angle to the length of the adjacent side.

\(tan(\theta)=\frac{Opposite side}{Adjacent side}​\)

d. Additional Ratios:

In addition to these primary ratios, there are reciprocal trigonometric ratios:

  • Cosecant (csc): \(csc(\theta)=\frac{1}{sin (\theta)}\)
  • Secant (sec): \(sec(\theta)=\frac{1}{cos (\theta)}\)
  • Cotangent (cot): \(cot(\theta)=\frac{1}{tan (\theta)}\)

Unit Circle Interpretation:

Trigonometric ratios can also be understood geometrically using the unit circle. The unit circle is a circle with a radius of 1 unit centered at the origin of a coordinate system. The coordinates of a point on the unit circle correspond to the values of cosine and sine for a particular angle.

  • On the unit circle, the \(x-\)coordinate is the cosine (cos) of the angle.
  • The \(y-\)coordinate is the sine (sin) of the angle.

4. Trigonometric Identities:

Trigonometric identities are equations involving trigonometric functions that are true for all values of the variables. Some essential identities include the Pythagorean identities:




These identities are derived from the Pythagorean theorem and play a crucial role in simplifying trigonometric expressions.

5. Calculating Trigonometric Ratios:

When working with a specific angle in a right-angled triangle, you can calculate the trigonometric ratios using the lengths of the sides. For example, if you know the lengths of the opposite \(O\) and hypotenuse \(H\) sides, you can find the sine:


Similar formulas apply for cosine and tangent using the adjacent \(A\) side.


Trigonometric ratios find applications in various fields such as physics, engineering, navigation, computer graphics, and architecture. They are used to analyze angles, distances, forces, and periodic phenomena.

In summary, trigonometric ratios are essential tools for understanding and solving problems related to triangles and have broad applications in both theoretical and practical aspects of mathematics and other disciplines.

6. Applications in Real Life:

a. Physics:

Trigonometry is used to analyze forces, motion, and waves.

b. Engineering:

Engineers apply trigonometric principles in designing structures and analyzing mechanical systems.

c. Navigation:

Navigators use trigonometry to determine positions and plan routes.

d. Computer Science:

Trigonometry is vital in computer graphics for modeling and rendering.

e. Architecture:

Architects use trigonometry to ensure precision in measurements and designs.

7. Conclusion:

Understanding trigonometric ratios is essential for solving a wide range of mathematical problems and has far-reaching applications in various fields. As you explore the intricacies of trigonometry, remember that these ratios are not just abstract mathematical concepts but powerful tools with real-world significance. Mastery of trigonometric ratios opens the door to a deeper understanding of the relationships between angles and sides in the fascinating realm of triangles.