This was one of the "pioneer" websites for student solutions. While many students used it to quickly copy answers, many others used it as a self-check tool to understand complex problem-solving steps.
They are using legacy practice problems that remain relevant for general mathematical understanding. Important Note
Yu. N. Makarychev’s algebra textbooks are a standard for Russian middle schools. The 9th-grade curriculum typically covers quadratic functions, equations and systems of equations, power functions, and elements of combinatorics and probability.
If you are currently a student, it is worth noting that modern versions of this textbook now include more preparation for the (State Compulsory Exam). Using a 2010 solution key for a 2023 textbook might lead to a "mismatch" in problem numbers.