Tyler Wallace's "Beginning and Intermediate Algebra: Section 6.4: Factoring - Trinomials Where a ≠ 1"
Read this section. When we multiply polynomials we are distributing across parentheses. Here we are doing the reverse: We are trying to write a polynomial as a product of factors. We will introduce several techniques, and you should focus on learning them all because later it will be up to you to match the correct technique to a given problem.
Click https://s3.amazonaws.com/saylordotorg-resources/wwwresources/site/wp-content/uploads/2011/12/SAYLOR-MA001-TEXT.pdf link to open resource.