How do you solve #x^2+4x-12=0#?
Factorise this quadratic trinomial first.
Find factors of 12 which subtract (because of the MINUS) to make 4.
The correct factors will be
Their signs must be DIFFERENT (because of the MINUS 12)
The greater must be positive (because of the PLUS 4)
Now either of the two factors can be 0, to give the product of 0.