\(A-B=\left(\dfrac{2}{5}-\dfrac{3}{5}\right)x^2y^2z+\left(\dfrac{4}{3}+\dfrac{2}{3}\right)x^2y+\left(2xy-2xy\right)-5+1\)
\(=-\dfrac{1}{5}x^2y^2z+2x^2y-4\)
Tại x=-1;y=2;z=1
\(A=-\dfrac{1}{5}.\left(-1\right)^2.2^2.1+2.\left(-1\right)^2.2-4=-\dfrac{4}{5}\)