$B\,=(x-1)(-3x+1)-(3x-2)(2x-1)\\\quad =[x(-3x+1)-1(-3x+1)]-[3x(2x-1)-2(2x-1)]\\\quad =[-3x^2+x+3x-1]-[6x^2-3x-4x+2]\\\quad =(-3x^2+4x-1)-(6x^2-7x+2)\\\quad =-3x^2+4x-1-6x^2+7x-2\\\quad =-9x^2+11x-3$
Thay $x=\dfrac{2}{11}$ vào biểu thức $B=-9x^2+11x-3$
$B\,=-9.\left(\dfrac{2}{11}\right)^2+11.\dfrac{2}{11}-3\\\quad =-9.\left(\dfrac{4}{121}\right)+2-3\\\quad =\dfrac{-36}{121}-1\\\quad =-\dfrac{157}{121}$
Vậy $B=-\dfrac{157}{121}$ với $x=\dfrac{2}{11}$
