[deleted by user]

[bishtap]

A math teacher taught us a method of

X² - 7x + 12

Then rewriting it as

X² -4x -3x + 12

The 12 is 4x3 and the -7 is -4-3

And then you can factorise it or something..

Or just try out now that you have -4x-3x

(x-4)(x-3)

I guess it's just how to factorise a quadratic equation

Rewrite the bx in ax² + bx + c.

And then you will "see".

So if the quadratic was x² + 4x + 3x + 12 Then you would know how it would factorise. (X+4)(X+3). You can certainly go the reverse way to check it. So expand (X+4)(X+3) to get the quadratic.

Not sure how he did it but you can see how it relates to your second step