I have a mathematical question and solution which is taken from a different website. Can I post it here and ask specific queries on the part which I did not understand?
Mathematical ideas are exempt from patenting. Copyright covers only the "reduction to fixed form" of an expression, and in the case that an idea admits of only one or very few forms of expression, a copyright does not give exclusive ownership or control of such expressions.
Short answer: You should avoid plagiarism (by giving credit to your sources), but you should not be concerned with mathematics per se being subject to copyright.
References to US Copyright Act
"In no case does copyright protection for an original work of authorship extend to any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work."
"Copyright law does not protect ideas, methods, or systems. Copyright protection is therefore not available for ideas or procedures for doing, making, or building things; scientific or technical methods or discoveries; business operations or procedures; mathematical principles; formulas or algorithms; or any other concept, process, or method of operation."
US Copyright Office, Ideas, Methods, or Systems, summarizing the above section of Copyright Act
Reference to International Copyright Treaties
"Copyright protection extends to expressions and not to ideas, procedures, methods of operation or mathematical concepts as such."