MathThe ProfessorIntermediate
Precalculus Trigonometry, a free math course on Tomo

Precalculus Trigonometry

Bridge the gap between triangle geometry and continuous waves. Learn how sine, cosine, and tangent power circular motion, periodic graphing, and algebraic identities for advanced math.

Like Duolingo, but for Precalculus Trigonometry. Tomo turns the whole topic into a game you play five minutes a day, until it actually sticks.

27 levels across 3 sections, about 54 minutes end to end, roughly 11 days at five minutes a day. It moves through Unlocking the Unit Circle, Graphing and Shaping Periodic Waves, and Solving Equations and Transforming Expressions. It assumes you already know the basics.

27 bite-size levelsAbout 5 minutes each

Free forever · No credit card · iPhone & Android

Penny the Protractor, the guide who teaches the Precalculus Trigonometry course
Precalculus Trigonometry
with Penny the Protractor
27
Levels
3
Sections
5
Min/day
What you'll learn

Key ideas in Precalculus Trigonometry

  • A unit circle has a radius of exactly one unit by definition
  • Radian value equals the subtended arc length along a unit circle
  • Radian measure eliminates arbitrary degree scaling factors
  • Arc length equals the circle radius multiplied by angle in radians
  • The formula s = r * theta requires angle measurement strictly in radians
  • Multiplying radius by radian angle bypasses 360-degree fractions
  • Pi radians represents a half-turn or a straight line across the circle
  • Fractions between 1/2 and 1 of pi naturally sit in Quadrant II
  • Fractions between 1 and 3/2 of pi naturally sit in Quadrant III
  • Fractions between 3/2 and 2 of pi naturally sit in Quadrant IV
  • Pi over 6 represents one-twelfth of a circle or one-third of a quadrant
  • Adding or subtracting full rotations of 2pi yields coterminal angles
  • Negative signs indicate clockwise rotation from the standard initial axis
  • Angles beyond 2pi wrap repeatedly around the circular coordinate plane
  • A hypotenuse of one eliminates division when computing adjacent and opposite sides
  • The horizontal displacement x corresponds directly to cosine on a unit circle
Why not just Google it

You've tried the other tabs

Wikipedia

Thirty open tabs. Four facts you actually kept.

YouTube

You watched. You nodded. By Sunday it was gone.

ChatGPT

One answer, then back to scrolling.

Online courses

Eight weeks. You meant to finish. You didn't.

Tomo gives Precalculus Trigonometry the Duolingo treatment: levels, streaks, and quick quizzes that test what you just learned. That game loop is what the tabs above never had, so it's the one you actually finish.

Try a question

Here's what playing it feels like

A real question from this course. Take your best guess.

Measuring Angles with Arc Length

You walk along the rim of a unit circle through a central angle of 2.5 radians. How far have you walked?

Get it right to open this lesson and 26 more in the app.

Course map

How to learn Precalculus Trigonometry, step by step

Go in order. 27 short levels across 3 sections, about 54 minutes in all, five minutes a day.

  1. 1

    Unlocking the Unit Circle

    • Radians and Circular Angle Measurement
    • The Unit Circle as a Coordinate Engine
  2. 2

    Graphing and Shaping Periodic Waves

    • Graphing Sine and Cosine as Oscillations
    • Phase Shifts and Tangent Discontinuities
    • Modeling Periodic Systems
  3. 3

    Solving Equations and Transforming Expressions

    • Inverse Functions and Multi-Valued Solutions
    • Algebraic Manipulation with Fundamental Identities
    • Angle Sum and Double-Angle Mechanics

3 sections · 8 units · 27 levels. Built to play, not to enroll.

Questions

Questions about Precalculus Trigonometry

  1. How do I learn Precalculus Trigonometry?

    Go in order: start with Unlocking the Unit Circle, then Graphing and Shaping Periodic Waves, then Solving Equations and Transforming Expressions. On Tomo that's 27 short levels, about 54 minutes in all, played five minutes a day. Start free and play the first level in under a minute.

  2. Is there a Duolingo-style app for Precalculus Trigonometry?

    Yes. Tomo works like Duolingo: short daily lessons, streaks and quick quizzes. Precalculus Trigonometry is one of its free courses, and you can type any other topic to get a course of your own.

  3. Is the Precalculus Trigonometry course free?

    Yes. Precalculus Trigonometry is playable on Tomo's free plan, which doesn't expire. No credit card, no waitlist. Download the app and start your first lesson.

  4. How long does it take to learn Precalculus Trigonometry?

    27 levels across 3 sections, about 54 minutes of play in total. It's built for five minutes a day, so you finish it a little at a time instead of all at once.

  5. Do I need any background to start Precalculus Trigonometry?

    No. It's pitched at an intermediate level, so it starts where you are and builds up. If you can tap a phone, you can start.

New

Tomo is in ChatGPT

Tomo is also a ChatGPT plugin: the same playable courses, built and played inside your chat.

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How it's taught

You pick the voice

This course
The Professor

Precalculus Trigonometry is taught in the Professor style: clear, structured, thorough. Want a different feel? In the app you can spin up the same topic in any of Tomo's teaching styles. Same facts, totally different vibe.

Start free

Start Precalculus Trigonometry today.

Download Tomo, search Precalculus Trigonometry, and play your first lesson in under a minute.