Search on the website of the school library: Many universities provide online library services, which usually include searching for electronic textbooks. Log on to your school library website and use search tools to find electronic textbooks.
Online educational resources website search: Some websites provide a large number of free educational resources, including electronic teaching materials. Some well-known online educational resources websites include Coursera, edX, Khan Academy, etc.
Search in online bookstores or online retailers: Some online bookstores or online retailers offer the service of purchasing or renting electronic textbooks. Search these websites for the required teaching materials to see if there is an electronic version.
Ask a professor or classmate: Sometimes the professor will provide links or information of electronic teaching materials in the course introduction or class. You can also ask your classmates or seniors if they have copies of electronic textbooks.
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It should be noted that the copyright of electronic textbooks is still protected, and it is illegal to download and distribute them without permission.