Cho 2 đa thức P(x)=3 x mũ 3 trừ 2 x cộng 1 Q( x) bằng 3 x mũ 2 trừ 2 x mũ 3 cộng x trừ 5 18/08/2021 Bởi aikhanh Cho 2 đa thức P(x)=3 x mũ 3 trừ 2 x cộng 1 Q( x) bằng 3 x mũ 2 trừ 2 x mũ 3 cộng x trừ 5
a) $P(1)=3.1^3-2.1+1=3.1-2+1=3-2+1=2$ $Q(-1)=3.(-1)^2-2.(-1)^3-1-5=3.1+2-1-5=3+2-1-5=-1$ b) $P(x)+Q(x)=(x^3-2x+1)+(3x^2-2x^3+x-5)$ $P(x)+Q(x)=x^3-2x+1+3x^2-2x^3+x-5$ $P(x)+Q(x)=(x^3-2x^3)+3x^2+(-2x+x)+(1-5)$ $P(x)+Q(x)=-x^3+3x^2-x-4$ $P(x)-Q(x)=(x^3-2x+1)-(3x^2-2x^3+x-5)$ $P(x)-Q(x)=x^3-2x+1-3x^2+2x^3-x+5$ $P(x)-Q(x)=(x^3+2x^3)-3x^2+(-2x-x)+(1+5)$ $P(x)-Q(x)=3x^3-3x^2-3x+6$ Bình luận
a) $P(1)=3.1^3-2.1+1=3.1-2+1=3-2+1=2$
$Q(-1)=3.(-1)^2-2.(-1)^3-1-5=3.1+2-1-5=3+2-1-5=-1$
b) $P(x)+Q(x)=(x^3-2x+1)+(3x^2-2x^3+x-5)$
$P(x)+Q(x)=x^3-2x+1+3x^2-2x^3+x-5$
$P(x)+Q(x)=(x^3-2x^3)+3x^2+(-2x+x)+(1-5)$
$P(x)+Q(x)=-x^3+3x^2-x-4$
$P(x)-Q(x)=(x^3-2x+1)-(3x^2-2x^3+x-5)$
$P(x)-Q(x)=x^3-2x+1-3x^2+2x^3-x+5$
$P(x)-Q(x)=(x^3+2x^3)-3x^2+(-2x-x)+(1+5)$
$P(x)-Q(x)=3x^3-3x^2-3x+6$