Purplemath
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Elizabeth Stapel's free lesson site covering pre-algebra through intermediate algebra, including equations, inequalities, graphing, polynomials, factoring, radicals, exponents and word problems. Each lesson works through examples step by step, explaining common mistakes and how to check answers.
More resources on Algebra
Introduction to Algebra
Learn the fundamentals of algebra with Richard Rusczyk's book! Master functions and essential algebraic concepts.
Wolfram Alpha
Computational knowledge engine that answers typed natural-language or symbolic queries by solving equations, factoring and simplifying expressions, and plotting functions. Students can check algebra work and inspect results, though full step-by-step solutions require a paid Pro subscription.
math.stackexchange.com
Math Stack Exchange is a community Q&A site for mathematics where users ask, answer, and discuss problems across topics from algebra to advanced theory. It features a large archive of math questions with detailed explanations, proofs, examples, and peer-voted high-quality answers.
artofproblemsolving.com
AoPS is a comprehensive mathematics learning community offering challenging problems, step-by-step solutions, and active forums, along with online courses and textbooks for competition math. It provides problem sets, tutorials, and classroom resources covering topics from fundamentals to advanced contest math.
Paul's Online Math Notes
Paul Dawkins's free algebra notes from Lamar University, covering preliminaries, solving equations and inequalities, graphing, functions, polynomials, exponential and logarithmic functions, and systems of equations. Worked examples and practice problems prepare students for calculus-level work.
Math is Fun - Pre-Algebra
Free illustrated reference site whose algebra section introduces variables, expressions, equations, inequalities, exponents and basic graphing through short explanations, worked examples and interactive quizzes, helping learners build intuition before formal algebra coursework.