Ответ:

(2х - 7)(х + 1) + 3(4х-1)(4х+1) = 2(5х - 2)^2 - 35

(2х - 7)(х + 1) + 3(16х^2 - 1) = 2(25х^2 - 20х + 4) - 35

2х^2 + 2х - 7х -7 + 48х^2 - 3 = 50х^2 - 40х + 8 - 35

2х^2 + 2х - 7х + 48х^2 - 50х^2 + 40х = 8 - 35 + 7 + 3

35х = -17

х= -17/35