Courses from 1000+ universities
AI got cheap enough that Duolingo’s most expensive plan may not survive it. I read the earnings call transcript and opened the app to see what is actually changing for learners.
600 Free Google Certifications
Computer Science
Artificial Intelligence
Data Science
Intelligenza Artificiale
The Bible's Prehistory, Purpose, and Political Future
Education for All: Disability, Diversity and Inclusion
Organize and share your learning with Class Central Lists.
View our Lists Showcase
Uses the wedge of two circles to illustrate covering spaces as directed, labeled 4-valent graphs, then introduces the universal cover.
Explore how free abelian groups resemble vector spaces, then see how non-commutativity changes cosets and leads to normal subgroups and quotient groups.
See how finite commutative groups decompose into cyclic groups, starting from the basic axioms and concrete examples.
A precise mathematical definition of sequences emerges through examples from natural numbers, primes, and rationals.
Trace how mechanics shaped the study of curves, from the catenary and cycloid to Euler’s elastica and Bézier control points.
Compare standard quadratic and cubic formulas with Newton’s method, showing how each approach produces approximate solutions.
Newton’s method turns tangent-line intersections into a recursive process for approximating square roots, illustrated with x² and √2.
Explore addition with small numbers, then compare English number names with an alternate system and organize the results in addition tables.
See how polyominoes are counted and classified, then use checkerboard coloring to explore when trominoes and tetrominoes can tile a grid.
See how translations and reflections in the grid plane reveal the commutative laws for addition and multiplication.
See how loop classes acquire group structure through multiplication, identity, inverses, and associativity, with examples from the torus and projective plane.
See how Seifert surfaces are built for knots and how adding boundary cuffs changes a surface’s Euler number.
Classify surfaces by cutting and pasting their polygons into standard forms with handles and crosscaps.
Uses winding numbers of polynomial images of concentric circles to give a geometric proof of the Fundamental Theorem of Algebra.
Introduces a rational turn-angle measure for polygons, then uses winding and turning numbers to describe planar curves.
Get personalized course recommendations, track subjects and courses with reminders, and more.