why can't you solve a quadratic such as
X=-6 and -11 (I know these aren't the real solutions)
To use factorising to solve a quadratic you have to have a zero on one side. Then you know for sure that one of the factors must be zero.
x can be either -2 or -3, because when you substitute either of these values into the equation, one of the brackets will become zero. and as you know, anything multiplied by zero is also.