Bạn tham khảo:
$6x (3x+5) - 2x (3x-2) + (17-x) (x-1) + x (x-18) =0$
$=18x^2 + 30x - 6x^2 - 4x + 17x + 17 + x^2 + x - x^2 - 18x = 0$
$= 18x^2 + 30x + 17x - 4x - 18x+ x^2 - x^2 + x =0$
$ =18x^2 + 25 + 0 + x = 0$
$=18x^2 + x + 25 = 0$
$= 18x^2 + x = -25$