How to Find the Exact Value of a Trig Function – Quick and Easy Guide

How to Find the Exact Value of a Trig Function Quick and Easy Guide

To find the exact value of a trigonometric function, I first consider the specific angle in question. Some angles, like $30^\circ$, $45^\circ$, and $60^\circ$, have well-known exact values for sine, cosine, and tangent functions, which are derived from specific right triangles.

I refer to the unit circle, where the circumference represents angles in radians, and position coordinates correspond to the values of the trigonometric functions at that angle.

Understanding the symmetries and periodic properties of the trigonometric functions allows me to determine exact values for a wider range of angles.

By applying certain identities, such as the Pythagorean identity or angle sum and difference formulas, I can find the trigonometric values for other angles not immediately found on the unit circle. 

Steps Involved in Finding the Exact Values for Trigonometric Functions

To find the exact values for trigonometric functions such as sin, cos, and tan, I follow a structured approach. Here’s how I do it:

  1. Identify the Angle: First, I determine the angle in degrees or radians. If necessary, I convert between degrees and radians using the formula: $$ \text{Radians} = \text{Degrees} \times \frac{\pi}{180} $$

  2. Reference Angles: I find the reference angle, which is the acute angle that the terminal side of my given angle makes with the x-axis. This simplifies calculations, especially for angles greater than $90^\circ$ (or $\frac{\pi}{2}$ radians).

  3. Quadrants and Signs: The sign of a trigonometric function depends on which quadrant the angle lies in:

  4. Special Angles and Unit Circle: I consider special angles that have known exact values on the unit circle, such as $0^\circ$, $30^\circ$, $45^\circ$, $60^\circ$, and v90^\circ$; or in radians: (0), $\frac{\pi}{6}$, $\frac{\pi}{4}$, $\frac{\pi}{3}$, and $\frac{\pi}{2}$. The coordinates of these angles on the unit circle correspond to the values of cos and sin, respectively.

  5. Trigonometric Identities: I employ trigonometric identities to evaluate trigonometric functions. For instance, the Pythagorean identity: $$ \sin^2(\theta) + \cos^2(\theta) = 1 $$

By using a combination of these approaches, I effectively find exact trigonometric values for angles. Remember, practice helps to reinforce these concepts and improve the speed and accuracy of calculations.

Practical Tips and Tools

Finding the exact values of trigonometric functions can be simplified by using a combination of practical tools and memorization techniques. Here’s how I approach it:

Calculators: A scientific calculator is an indispensable tool for checking work. Make sure it’s set to the correct mode (degrees or radians) to match the problem you are working on.

Memorization: I find it useful to commit to memory the values of sine, cosine, and tangent for common angles such as $0, \frac{\pi}{6}, \frac{\pi}{4}, \frac{\pi}{3}$, and $\frac{\pi}{2}$. This is a small list that can significantly speed up calculations.

Angle (Radians)$\sin$$\cos$$\tan$
( 0 )( 0 )( 1 )( 0 )
$\frac{\pi}{6} $$ \frac{1}{2} v$\frac{\sqrt{3}}{2}$$ \frac{1}{\sqrt{3}} $
$\frac{\pi}{4}$$\frac{\sqrt{2}}{2}$$\frac{\sqrt{2}}{2}$( 1 )
$\frac{\pi}{3} $$ \frac{\sqrt{3}}{2}$$\frac{1}{2}$$\sqrt{3}$

Articles and Lists: I often refer to articles and lists online that provide the trigonometric equations and properties. This is useful when dealing with more complex problems in algebra and calculus, especially when exploring the domains of these functions.

Algebraic Techniques: Familiarity with algebraic manipulations can also help solve for trigonometric values. I work through algebraic expressions using identities like the Pythagorean identity $ \sin^2(x) + \cos^2(x) = 1 $ or angle sum and difference formulas.

Calculus Applications: For those exploring calculus, understanding the integrals and derivatives of trigonometric functions is crucial. This knowledge often provides insights into the behavior of these functions across different domains.


In this guide, I walked through the process needed to find the exact values of trigonometric functions. To recap, let’s consider the essential steps for achieving such values:

  1. Identify the angle in question and relate it to the unit circle.
  2. Apply relevant trigonometric identities such as the Pythagorean identity, $\sin^2(\theta) + \cos^2(\theta) = 1$, when needed.
  3. Reference common angles, like $30^\circ$, $45^\circ$, and $60^\circ$, and their radian conversions.
  4. Utilize periodicity properties—for sine and cosine, the value repeats every $2\pi$ radian. In other words, $\sin(\theta) = \sin(\theta + 2k\pi)$ and $\cos(\theta) = \cos(\theta + 2k\pi)$, where $k$ is any integer.
  5. Apply co-function identities, such as $\sin(90^\circ – \theta) = \cos(\theta)$, when dealing with complementary angles.

As you become more familiar with these strategies, your ability to find the exact trigonometric values will improve. Be sure to practice with a variety of angles and problems to build your confidence and proficiency.

Remember, understanding the geometrical interpretations of these functions can also immensely clarify their exact values.

By consistently using these methods, you’ll be able to swiftly and accurately determine the trigonometric values you need, whether for academic purposes, problem-solving, or real-world applications