Step-1 : Multiply the coefficient of the first term by the constant 3 • -20 = -60
Step-2 : Find two factors of -60 whose sum equals the coefficient of the middle term, which is -11 .
-60 + 1 = -59
-30 + 2 = -28
-20 + 3 = -17
-15 + 4 = -11
That's it
Step-3 : Rewrite the polynomial splitting the middle term using the two factors found in step 2 above, -15 and 4
3x2 - 15x + 4x - 20
Step-4 : Add up the first 2 terms, pulling out like factors :
3x • (x-5)
Add up the last 2 terms, pulling out common factors :
4 • (x-5)
Step-5 : Add up the four terms of step 4 :
(3x+4) • (x-5)
Which is the desired factorization
