Câu 2:
$3x^4y.\frac{1}{6}x^2z$
$=3.\frac{1}{6}.x^4y.x^2z$
$=\frac{1}{2}x^6yz$
Khi $x=2; y=-1; z=3$, ta có:
$\frac{1}{2}.2^6.(-1).3=-96$
Câu 3:
a,
$P(x)= -4x^5+x^3+x^2-2x-12$
$Q(x)= -4x^5+x^3+x^2-7x+3$
b,
$N(x)= -4x^5+x^3+x^2-2x-12+4x^4-x^3-x^2+7x-3$
$= 5x-15$
c,
$N(x)=0 \Rightarrow 5x-15=0$
$\Leftrightarrow x=5$
Câu 5, 6 (như hình)