(b-7)(b+4)-(b+2)(b+1) = (b²+4b-7b-28)-(b²+b+2b+2) = b²+4b-7b-28-b²-b-2b-2 = 4b-7b-28-b-2b-2 = -6b-30
если b = -1/3, то
-6b-30 = -6(-1/3)-30 = 2-30 = -28
(b-7)(b+4)-(b+2)(b+1) = (b²+4b-7b-28)-(b²+b+2b+2) = b²+4b-7b-28-b²-b-2b-2 = 4b-7b-28-b-2b-2 = -6b-30
если b = -1/3, то
-6b-30 = -6(-1/3)-30 = 2-30 = -28