7x – 6x2 + 20 = - 6x2 + 7x + 20
Here, coefficient of x2 = -6, coefficient of x = 7 and constant term = 20
We shall now split up the coefficient of x i.e., 7 into two parts whose sum is 7 and product is -6 x 20 = - 120
Clearly,
15 - 8 = 7 and
15 (-8) = - 120
So, we write middle term 7x as 15x - 8x
Thus, we have
-6x2 + 7x + 20 = -6x2 + 15x - 8x + 20
= -3x (2x – 5) - 4 (2x – 5)
= - (3x + 4) (2x - 5)