`a)`
`C=A*B`
`=(1/3x^2y^3z)*(-4/3x^3yz^2)`
`=(1/3*-4/3)*(x^2*x^3)*(y^3*y)*(z*z^2)`
`=-4/9x^(2+3)*y^(3+1)*z^(1+2)`
`=-4/9x^5y^4z^3`
`b)` Thay `x=-1,y=2,z=-3` vào `C` ta được:
`C=-4/9*(-1)^5*2^4*(-3)^3`
`=-4/9*(-1)*16*(-27)`
`=-4/9*16*27`
`=-4*16*3`
`=-12*16`
`= -192`
Vậy: `C=-192` khi `x=-1,y=2,z=-3`

