---
title: Trigonometric Functions
description: Trigonometric functions relate the angles of a right triangle to ratios of its sides. Learners will understand sine, cosine, tangent, and their reciprocals, including how to graph these periodic functions and model real-world cyclical phenomena.
category: mathematics
subcategory: geometry-and-trigonometry
difficulty: beginner, intermediate, advanced
url: /subject/trigonometric-functions
---

# Trigonometric Functions

Trigonometric functions relate the angles of a right triangle to ratios of its sides. Learners will understand sine, cosine, tangent, and their reciprocals, including how to graph these periodic functions and model real-world cyclical phenomena.

## Available Resources

1 Books • 1 Courses • 4 Websites

## Websites

### 1. Math is Fun - Trigonometry

Illustrated introduction to right-triangle trigonometry from the Math is Fun site. It defines sine, cosine and tangent as side ratios, introduces the unit circle and common angles, and works simple examples so learners can find missing sides and angles in triangles.

**Difficulty:** Beginner | **Price:** Free

**Link:** https://www.mathsisfun.com/algebra/trigonometry.html

**Tags:** trigonometry, sine-cosine-tangent, right-triangles, unit-circle

### 2. Paul's Online Math Notes - Trig

Review section from Paul Dawkins' Calculus I notes at Lamar University. It recaps radians, the unit circle, the six trig functions, their graphs and periodicity, and evaluating them at standard angles, with worked examples that prepare learners for trigonometry inside calculus.

**Difficulty:** Beginner | **Price:** Free

**Link:** https://tutorial.math.lamar.edu/classes/calcI/trigfcns.aspx

**Tags:** trigonometry, unit-circle, radians, trig-functions, precalculus

### 3. Wolfram MathWorld

**Author:** Eric W. Weisstein

MathWorld is an online mathematics encyclopedia from Wolfram Research offering detailed, browsable articles on topics across the math spectrum, including algebra, geometry, calculus, and number theory. Each entry includes definitions, theorems, formulas, diagrams, worked examples, and links to further reading.

**Difficulty:** Intermediate | **Language:** English | **Price:** Free

**Link:** https://mathworld.wolfram.com

**Tags:** mathematics-reference, encyclopedia, abstract-algebra, number-theory, geometry

### 4. mathsisfun.com

MathIsFun.com is a beginner-friendly math site that explains concepts with clear, step-by-step lessons and interactive activities. It covers topics from algebra and linear equations to geometry, fractions, data, and more, with practice problems, worksheets, and quizzes.

**Difficulty:** Intermediate | **Language:** English | **Price:** Free

**Link:** https://mathsisfun.com

**Tags:** websites, mathematics-statistics, algebra

## Courses

### 1. Trigonometry Khan Academy

Master law of sines & cosines with Sal Khan's free Trigonometry course! Ace triangles & trigonometry calculations.

**Difficulty:** Beginner | **Price:** Free

**Link:** https://www.khanacademy.org/math/trigonometry

**Tags:** trigonometry, law-of-sines, law-of-cosines, unit-circle

## Books

### 1. Trigonometry

**Author:** I. M. Gelfand, Mark Saul

A short, problem-driven text from the Gelfand School Outreach Program that builds trigonometric functions from geometry, then treats them as functions in their own right. Readers learn addition formulas, identities, and graphs and come away prepared for calculus.

**Difficulty:** Intermediate | **Language:** English | **Price:** Paid

**Link:** https://www.amazon.com/dp/0817639144?tag=edmonddante07-20

**Tags:** books, mathematics-statistics, geometry--trigonometry

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