CK-12: Free, quality math and science curriculum
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This site features textbooks in a flexible format called "Flexbooks" available for free download and printing. Most programs include a Teacher's Edition, workbooks, and other supplementary material, all for free. The topics at the moment include middle school and high school level math and science. The science is mainstream (evolution is included in Life Science and Biology programs). The Chemistry course includes labs. The math is fairly traditional and includes Algebra, Geometry, Trigonometry, Probability & Statistics (AP), and Calculus (AB). Free SAT prep books are also available on the site.
The site requires registration for full access, but the registration process is simple and free. Once you've registered, you can view textbooks online, print them as pdfs, or customize them, using only the chapters that interest you, and mixing and matching from different books. In addition to searching for complete textbooks on subjects, you can search for individual chapters within the many books on the site.
