Lessons for school
High-school topics explained the way a good tutor would: first the few rules you actually need, then a figure you can move with your own hands, then the exam questions solved step by step, then questions that check your answer. Everything runs in your browser, nothing is sent anywhere.
Mathematics
High-school mathematics, one topic at a time: the rules you need, a picture you can move, worked examples step by step, and practice questions that check your answer.
TrigonometryTriangles9 lessons Open mathematics →More subjects
Physics, chemistry and more are written in the same shape — rules, a moving figure, worked examples, practice. They appear here as they are ready. Meanwhile the tools (function plotter, physics simulations, chemistry calculator) already cover a lot of ground.
How a lesson works
Rules first. Every lesson opens with the handful of formulas the topic really needs, marked with which worked examples use them. See it. A figure you can drag, slide or animate — the angle on a unit circle, the vertices of a triangle — so the rule is something you have watched, not memorised. Worked examples. Real exam-style questions, each with a figure, a guiding question to ask yourself, the solution step by step and the answer. Solutions are folded so you can try first. Practice. Fresh questions generated every time, checked instantly, with the explanation when you miss one. Your best score stays in this browser.
Lessons are written for the content of high-school courses and are free to use without an account. Found a mistake? Tell us and we will fix it.