Arithmetic
Whole numbers, fractions, decimals and percentages: the number sense every later course relies on.
- Arithmetic Foundations · 3 topics
Subjects and courses
23 subjects, 26 courses and 73 topic explainers. Each topic page explains the idea in plain language, works a full example, lists the mistakes students make most and ends with practice questions you can check.
Mathematics
Pre-Algebra
Variables, expressions, integers, exponents and one-step equations: the bridge from arithmetic to algebra.
- Pre-Algebra · 3 topics
Algebra
Linear and quadratic equations, functions, inequalities, systems, polynomials, exponentials and logarithms.
Geometry
Angles, triangles, circles, area and volume, coordinate geometry and proof.
- Geometry · 4 topics
Trigonometry
Right-triangle ratios, the unit circle, identities, trigonometric equations and the laws of sines and cosines.
- Trigonometry · 3 topics
Precalculus
Functions and their graphs, transformations, inverses, composition, polynomial and rational functions, and sequences.
- Precalculus · 3 topics
Calculus
Limits, derivatives, integrals, series and multivariable ideas, with verified step-by-step work.
- Calculus 1 · 3 topics
- Calculus 2 · 2 topics
- Multivariable Calculus · 2 topics
Linear Algebra
Vectors, matrices, determinants, inverses, eigenvalues and eigenvectors.
- Linear Algebra · 3 topics
Differential Equations
Separable, linear first-order and constant-coefficient second-order equations with initial values.
- Differential Equations · 3 topics
Statistics
Describing data, the normal distribution, confidence intervals, correlation and regression.
- Introductory Statistics · 3 topics
Probability
Counting, probability rules, conditional probability and random variables.
- Probability · 3 topics
Discrete Math
Logic, sets, induction, number theory and graphs.
- Discrete Mathematics · 2 topics
Science
Physics
Kinematics, forces, energy, momentum and circuits, with formula calculators that show every step.
- Introductory Physics · 4 topics
Chemistry
Moles, molar mass, stoichiometry, solutions, gas laws and pH.
- General Chemistry · 4 topics
Biology
Cells, genetics, evolution and ecology, with quantitative skills such as Punnett squares and Hardy-Weinberg.
- Biology · 2 topics
Environmental Science
Ecosystems, resources, pollution and climate, with the unit conversions environmental questions need.
- Environmental Science · 2 topics
Computer Science
Computer Science
Computing concepts: binary, abstraction, the internet and the impact of computing.
- Computer Science Principles · 2 topics
Programming
Variables, conditionals, loops, functions and object-oriented design.
- Introduction to Programming · 2 topics
Data Structures
Arrays, lists, stacks, queues, trees, hash tables and graphs.
- Data Structures · 3 topics
Algorithms
Searching, sorting, recursion and Big-O analysis.
- Algorithms · 3 topics
Business and Economics
Accounting
The accounting equation, financial statements and ratios.
- Financial Accounting · 3 topics
Economics
Supply and demand, elasticity, market structures and macroeconomic indicators.
- Principles of Economics · 2 topics
Finance
Interest, time value of money, loans and investment returns.
- Finance Fundamentals · 3 topics