=x(3x? -4xy-7y? )
=x(3x-7y)(x+y) (cross multiplication)
3X ﹣7Y
× (schematic diagram of cross multiplication)
X Y
3x*x=3x? ﹣7y*y=﹣7y?
﹣7xy+3xy=﹣4xy
You can ask if you don't understand! Satisfied, please adopt it in time! O(∩_∩)O