2x^2 -x -28 = 2x^2 - 8x + 7x - 28 = 2x(x - 4) + 7(x - 4) = (2x + 7)(x - 4) I hope that the above factorization is absolutely clear for you to understand. I also hope that this is the answer that you were looking for and the answer has actually come to your desired help.
