we were working on factoring in class, which is a piece of cake, but my teacher showed us to do something i’ve never done before in my work with factoring.

#1 15xy+8+20x+6y

we switched the middle two so it could be factored easier:

15xy+20x+8+6y

5x(3y+4) + 2(4+3y)

(3y+4)(5x+2)

then, he did this on #2

6x^2 +14y-4xy-21x

switched the middle two:

6x^2-4xy+14y-21x

2x(3x-2y) + 7(2y-3x)

he said since the order of the 2y and 3x was different on both sides, you have to swith the sign to make them switch. so:

2x(3x-2y) – 7(3x-2y)

(3x-2y)(2x-7)

i’m not comprehending why he changed the sign on the second one and not the first one.

totally not in school mode yet.

thanks in advance!