(b^2-49)(b+1/b-7-b-1/b+7)-15b+7 =((b+7)(b-7))(b + 1/b - 7 - b - 1/b + 7) - 15b + 7 =(b^2 - 49)(b - b) - 15b + 7 =0 - 15b + 7 =-15b + 7
(b^2-49)(b+1/b-7-b-1/b+7)-15b+7 =
((b+7)(b-7))(b + 1/b - 7 - b - 1/b + 7) - 15b + 7 =
(b^2 - 49)(b - b) - 15b + 7 =
0 - 15b + 7 =
-15b + 7