A junior two student knelt down and asked for the cross multiplication. Not an answer that can be copied. I don't know why the teacher didn't say ~ the book is published by PEP, and it's not in the book. See if you can understand the following four questions:

Example 1 M? +4m- 12 factorization?

Analysis: The quadratic term in this question can only be divided into 1× 1, and the constant term-12 can be divided into-1× 12, -2×6, -3×4, -4×3 and-6× 4.

The quadratic term on the left and the constant term on the right are multiplied obliquely, and the sum of them is equal to the linear term.

1╳6

1╳-2

( 1×6)+( 1×-2)=4