Factoring Quadratic Expressions Using X-Box Method. This worksheet has a step by step example on how to use the x-box (aka: diamond box or just box) method along with a page of 14 practice problems and another page of blank problems that have the x and the box drawn out. I feel that the x-box method is the best way to teach students factoring. Oh, and make sure you explain what each letter stands for: F = First term, M = Middle term, L = Last term, a and b are just the factors of F x L and the sum of M. GCF means to take the greatest common factor from each row and column. Download the preview file to see exactly what you will get. Thank you.