2x^2 + 7x - 4
Multiply first term by the last term
2 * - 4 = -8
Find 2 factors of -8 whose sum equals the middle term (7)
8 x -1 = -8
8 - 1 = 7
Rewrite the polynomial
2x^2 -x +8x - 4
Add up first 2 factors and factor out
(2x^2 -x) (8x - 4 )
x (2x - 1) 4 (2x-1 )
Rewrite:
(2x-1 ) (x+4)