The biggest trouble in primary school mathematics investigation is cross multiplication. In the primary school mathematics survey in 2022, children's biggest worry is cross multiplication. Cross multiplication needs to split the equations one by one, requires strong understanding and calculation ability, and is extremely difficult for primary school students.

The method of cross multiplication is simply that the multiplication on the left side of the cross is equal to the quadratic term, the multiplication on the right side is equal to the constant term, and the multiplication and addition of the cross are equal to the linear term. In fact, it is factorization by multiplication formula operation. Cross-product is a very important knowledge in junior high school, which is not covered in the syllabus and textbooks in many places, but it is often used to solve quadratic equations in one variable and senior high school. Therefore, it is suggested that every junior high school student should master cross multiplication.